bahan_ajar_farmakokinetika-bu_farida.pdf

BAHAN AJAR

MATA KULIAH FARMAKOKINETIKA

Penyusun/Pengampu: M.M. Farida Lanawati Darsono, S.Si., M.Sc.

Universitas Katolik Widya Mandala FAKULTAS FARMASI

Surabaya

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Rencana Program dan Kegiatan Pembelajaran Semester (RPKPS) (Q-004)

Nama Mata Kuliah : Farmakokinetika Kode Mata Kuliah : PHR 470 (MKB) Pilihan/Wajib*) Semester : 7 Prasyarat : Biofarmasetika Jumlah SKS : 1 sks Kosyarat : - Program Studi : S 1 – Farmasi

Fakultas Farmasi Unika Widya Mandala Surabaya Tahun Akademik : 2014/2015/Semester Gasal

Tatatp Muka

Ke

Pokok Bahasan Dosen Pustaka

1 3 4 5 I Introduction to pharmacokinetics &

Pharmacokinetics versus route of delivery

Farida L.D.,M.Sc Shargel & Yu (1999)

II Distribution (I) Farida L.D.,M.Sc Shargel & Yu (1999)

III Distribution (II) Farida L.D.,M.Sc Rowland & Tozer (1989)

IV Drug – protein binding Farida L.D.,M.Sc Rowland & Tozer (1989)

V Kinetics of drug – protein binding Farida L.D.,M.Sc Gibaldi (1984)

VI Non Linear pharmacokinetics Farida L.D.,M.Sc Gibaldi (1984) VII Michaelis Menten Equation Farida L.D.,M.Sc Rowland & Tozer (1989)

VIII UTS IX Hepatic and biliary metabolism (I) Drs. Kuncoro Foe, Ph.D Rowland & Tozer (1989)

X Hepatic and biliary metabolism (II) Drs. Kuncoro Foe, Ph.D Shargel & Yu (1999)

XI Hepatic and biliary metabolism (III) Drs. Kuncoro Foe, Ph.D Shargel & Yu (1999)

XII Renal excretion (I) Drs. Kuncoro Foe, Ph.D Shargel & Yu (1999)

XIII Renal excretion (II) Drs. Kuncoro Foe, Ph.D Ritschel (1984) XIV Renal excretion (III) Drs. Kuncoro Foe, Ph.D Ritschel (1984) XV Introduction to multiple dosage regimen Drs. Kuncoro Foe, Ph.D Shargel & Yu (1999)

XVI UAS

References: 1. Gibaldi, M., 1984. Biopharmaceutics and Clinical Pharmacokinetics. Lea and Febiger, Philadelphia. 2. Ritschel, W.A., 1984. Graphic Approach to Clinical Pharmacokinetics. JP Prous Publishers. 3. Rowland, M. and Tozer, T.N., 1989. Clinical Pharmacokinetics. Lea and Febiger, Philadelphia. 4. Shargel, L. and Yu, A.B.C., 1999. Applied Biopharmaceutics and Pharmacokinetics. McGraw-Hill, Inc., New

York. PJMK, ttd Drs.Kuncoro Foe,Ph.D.,Apt

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Sistem penilaian

• Dosen 1 : MM Farida Lanawati Darsono, S.Si.,M.Sc

Σ tatap muka : 7 kali (sebelum UTS)* • Dosen 2 : Drs. Kuncoro Foe, G.Dip.Sc.,Ph.D.,Apt

Σ tatap muka : 7 kali (sesudah UTS) Nilai UTS dan UAS @ : 100 Nilai akhir : {(40 x UTS) + {60 x UAS)}/100 * Nilai UTS : 80 nilai ujian + 20 nilai tugas References (for all topic) • Gibaldi, M., 1984. Biopharmaceutics and Clinical Pharmacokinetics. Lea and Febiger,

Philadelphia. • Ritschel, W.A., 1984. Graphic Approach to Clinical Pharmacokinetics. JP Prous Publishers. • Rowland, M. and Tozer, T.N., 1989. Clinical Pharmacokinetics. Lea and Febiger, Philadelphia. • Shargel, L. and Yu, A.B.C., 1999. Applied Biopharmaceutics and Pharmacokinetics. McGraw-

Hill, Inc., New York • Shargel, L. and Yu, A.B.C., 1985. Biofarmasetika dan Farmakokinetika Terapan (edisi kedua).

Universitas Indonesia, Jakarta. • Shargel, L., Pong, S.W. and Yu, A.B.C., 2005. Applied Biopharmaceutics and

Pharmacokinetics. 5th ed, pp. 8, 96-97, 115, Prentice-Hall International Inc., New York. • Swarbick, J. and Boylan, J.C., 2002. Encyclopedia of Pharmaceutical Technology, 2nd edition,

Volume 1, pp. 156-170, Marcel Dekker, New York. • Wagner, J.C., 1971. Biopharmaceutic and Relevant Pharmacokinetics, 1st ed, pp. 115-120,

Drug Intelligence Publishers, Illionis. • Rani,S., Hiremath,R., Text–Book of Biopharmaceutical and Pharmacokinetics, Prism Books

Pvt. Ltd., Edn-2000 , pg: 28- 32 • Brahmankar, D.M., Jaiswal, S.B., Biopharmaceutics & Pharmacokinetics A Treatise, Vallabh

Prakashan, Edn-2008, pg : 6-59, 75-88 • Gibaldi, M. , Pharmacokinetics, Marcel Dekker Inc., New York, 1982 , Edn - 2nd , pg – 44 – 48 • D.J. Birkett, Professor of Clinical Pharmacology, Flinders University of South Australia,

Adelaide (Aust Prescr 1994;17:36-8) • http://www.wisegeek.com/what-is-protein-binding.htm • http://www.nottingham.ac.uk/nmp/sonet/rlos/bioproc/plasma_proteins/6.html • etc

http://www.wisegeek.com/what-is-protein-binding.htm

BAHAN AJAR : FARMAKOKINETIKA DOSEN : Farida Lanawati Darsono,S.Si.,M.Sc

Topic 1 : Introduction and Routes of Administration • Drug molecules interact with target sites to effect the nervous system

– The drug must be absorbed into the bloodstream and then carried to the target site(s) • Pharmacokinetics is the study of drug absorption, distribution within body, and drug

elimination – Absorption depends on the route of administration – Drug distribution depends on how soluble the drug molecule is in fat (to pass through

membranes) and on the extent to which the drug binds to blood proteins (albumin) – Drug elimination is accomplished by excretion into urine and/or by inactivation by

enzymes in the liver Routes of Administration Movement of substances across cell membranes Passive diffusion • Also known as non-ionic diffusion. • It is defined as the difference in the drug concentration on either side of the membrane. • Absorption of 90% of drugs. • The driving force for this process is the concentration or electrochemical gradient. Facilitated diffusion of glucose Active transport Ion pair transport It is another mechanism is able to explain the absorption of such drugs which ionize at all pH condition The sodium-potassium pump ENDOCYTOSIS It involves engulfing extracellular materials within a segment of the cell membrane to form a saccule or a vesicle (hence also called as corpuscular or vesicular transport) which is then pinched off intracellularly. Endocytosis • During endocytosis, cells take in substances by invaginating a portion of the plasma membrane,

and forming a vesicle around the substance. • Endocytosis occurs as: • Phagocytosis – large particles • Pinocytosis – small particles • Receptor-mediated endocytosis – specific particles Exocytosis Pinocytosis Receptor-mediated endocytosis

Do not cited this article without permittion from Ms. Farida

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rute pemberian obat nasib obat di dalam tubuh • Pelakuan tubuh terhadap obat ada 4 proses :

1. Absorpsi : masuknya obat kedalam darah (gastrointestinal, bukal,rektal,pulmonal) 2. Distribusi: penyebaran obat keseluruh tubuh mengikuti sistem peredaran darah. 3. Metabolisme : transformasi struktur obat dg jalan oksidasi, reduksi,hidrolisis atau konjugasi

(hepar) 4. Ekskresi : pengeluaran obat dari dalam tubuh (ginjal dan hepar) + kelenjar lain.

• Parameter kinetik , berguna utk: cara pemakaian obat,monitoring efek obat dan membandingkan kwalitas obat A. Oral (PO)

Advantages: Convenient - portable, safe, no pain, easy to take. Cheap - no need to sterilize (but must be hygienic of course), compact, multi-dose bottles, automated machines produce tablets in large quantities. Variety of dosage forms available - fast release tablets, capsules,enteric coated, layered tablets, slow release, suspensions, mixtures Disadvantages: Sometimes inefficient - high dose or low solubility drugs may suffer poor availability, only part of the dose may be absorbed.

B. Buccal and Sublingual (SL)

Advantages: First pass - The liver is by-passed thus there is no loss of drug by first pass effect for buccal or sublingual administration. Bioavailability is higher. Rapid absorption - Because of the good blood supply to the area of absorption is usually quite rapid, especially for drugs with good lipid solubility. Drug stability - pH in mouth relatively neutral (cf. stomach - acidic). Thus a drug may be more stable. Disadvantages: Holding the dose in the mouth is inconvenient. If any part of the dose is swallowed that portion must be treated as an oral dose and subject to first pass metabolism. Usually more suitable for drugs with small doses. Drug taste may need to be masked.

C. Rectal (PR)

Advantages: By-pass liver - Some (but not all) of the veins draining the rectum lead directly to the general circulation thus by-passing the liver. Therefore there may be a reduced first-pass effect. Useful - This route may be most useful for patients unable to take drugs orally or with younger children. Disadvantages: Erratic absorption - Drug absorption from a supppository is often incomplete and erratic. Not well accepted. May be some discomfort.

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D. Intravenous (IV) Advantages:

• Rapid - A quick response is possible. Plasma concentration can be precisely controlled using IV infusion administration.

• Total dose - The whole dose is delivered to the blood stream. That is the bioavailability is generally considered to 100% after IV administration. Larger doses may be given by IV infusion over an extended time. Poorly soluble drugs may be given in a larger volume over an extended time period.

• Veins relatively insensitive - to irritation by irritant drugs at higher concentration in dosage forms.

Disadvantages: • Suitable vein - It may be difficult to find a suitable vein. There may be some tissue damage

at the site of injection. • Maybe toxic - Because of the rapid response, toxicity can be a problem with rapid drug

administrations. For drugs where this is a particular problem the dose should be given as an infusion, monitoring for toxicity.

• Requires trained personnel - Trained personnel are required to give intravenous injections. • Expensive - Sterility, pyrogen testing and larger volume of solvent means greater cost for

preparation, transport and storage.

E. Subcutaneous (SC) Advantages: Can be given by patient, e.g. in the case of insulin. Absorption can be fast from aqueous solution but slower with depot formulations. Absorption is usually complete. Improved by massage or heat. Vasoconstrictor may be added to reduce the absorption of a local anesthetic agent, thereby prolonging its effect at the site of interest. Disadvantages: Can be painful. Finding suitable sites for repeat injection can be a problem. Irritant drugs can cause local tissue damage. Maximum of 2 ml injection thus often small doses limit use.

F.Intramuscular (IM)

Advantages: Larger volume than SC can be given by IM. They may be easier to administer than IV injections. A depot or sustained release effect is possible with IM injections, e.g. procaine penicillin. Disadvantages: Trained personnel required for injections. The site of injection will influence the absorption, generally the deltoid muscle provides faster and more complete absorption. Absorption can be rapid from aqueous solution. Absorption is sometimes erratic, especially for poorly soluble drugs, e.g. diazepam, phenytoin. The solvent maybe absorbed faster than the drug causing precipitation of the drug at the site of injection. Irritiating drug may be painful.

G. Inhalation

• May be used for a local effect, e.g. bronchodilators. • Can be used for systemic effect, e.g. general anesthesia. • Rapid absorption by-passing the liver.


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• Absorption of gases is relatively efficient, however solids and liquids are excluded if larger

than 20 micron and even then only 10 % of the dose may be absorbed. Cromolyn is taken as a powder with 50 % of the particles within the range of 2 to 6 micron. Larger than 20 micron and the particles impact in the mouth and throat. Smaller than 0.5 micron and they aren't retained. Some portion of the dose may be swallowed

I. Topical or Transdermal

• Local effect - ear drops, eye drops or ointment, antiseptic creams and oinments, sunscreens, callous removal products, etc.

• Systemic effect - e.g., nitroglycerin ointment. • Generally absorption is quite slow. Absorption through the skin especially via cuts and

abrasions or from sites were the skin is quite thin can be quite marked. This can be a real problem in handling toxic materials in the laboratory or pharmacy. This can also be a serious problem with garden chemicals.

• An occlusive dressing may be used to improve absorption. • Transdermal patches can provide prolonged or controlled (iontrophoresis) drug delivery.

J. Other ROA's Other routes of administration include:

• nasal, some systemic absorption has been demonstrated for propranolol and some low dose hormones;

• intra-arterial for cancer chemotherapy to maximize drug concentrations at the tumor site; • intrathecal directly into the cerebrospinal fluid. • Others routes with limited systemic absorption but with local utility include topical, ocular,

aural, vaginal, urethral and intrasynovial


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BAHAN AJAR : FARMAKOKINETIKA

DOSEN : Farida Lanawati Darsono,S.Si.,M.Sc Topic 2 : Drug Distribution point

• To understand and describe the process by which drugs are distributed throughout the body • To understand the effect of protein binding on drug distributed

drug distribution patterns: 4 types • The drug may remain largely within the vascular system (ex: dextran ~plasma/drugs which stronglybound tp plasma) • Some low molecular weight water soluble compounds (become uniformly distributed throughout the body water) - (ex: ethanol / a few sulfonamide) • A few drugs are concentrated specifically in one or more tissues that may or may not be the site

of action (ex:iodine~thyroid glands/chloroquine~liver 1000x than present in plasma/tetracycline

~irreversible bound to bone & developing teeth ) • Most drugs exhibit a non-unifrorm distribution in the body with variations that are largely

determined by the ability to pass through membranes and their lipid/water solubility (ex: the highest concentrations are often present in the : kidney, liver, intestine)

Nb:

• pattern 4 is the most common being a combination of patterns 1,2 and 3 • Distribution of various substances within the body is NOT HOMOGENOUS

definition : distribution • Distribution: Movement of drug from the central compartment (blood) to peripheral

compartments (tissues) where the drug is present. • Distribution of a drug from systemic circulation to tissues is dependent on lipid solubility ,

ionization, molecular size , binding to plasma proteins , rate of blood flow and special barriers • The body compartments include extracellular (plasma, interstitial) and intracellular which are

separated by capillary wall and cell membrane • Distribution: the passage of drugs from blood to tissues. Distribution ---- where do drugs go? Once a drug has gained excess to the blood stream, the drug is subjected to a number of processes called as Disposition Processes that tend to lower the plasma concentration. 1. Distribution which involves reversible transfer of a drug between compartments. 2. Elimination which involves irreversible loss of drug from the body. It comprises of

biotransformation and excretion. Diffusion and hydrostatic pressure a. Passive diffusion : gradient conc --- fick’s law

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b. Hydrostatic pressure : (*) a pressure gradient between the arterial and of the capillaries entering the tissue and the

venous capillaries leaving the tissue (*) resonsible for penetration of water soluble drugs into spaces, between endothelial celss &

possible into lymph


The important factors in dtermining the rate of drug diffusion are :

The membranes thickness Diffusion coefficient of the drugs Concentration gradient across the capillaries membranes

Factor affecting drug distribution a. Rate of distribution :

membranes permeability blood perfussion

b. Extent of distribution lipid solubility pH – pka plasma protein binding intracellular binding

c. Tissue size d. Tissue storage

Rate limiting of distribution (tahap penetu kecepatan distribusi) a. Drug --- diffuse rapidly -----blood flow : perfussion rate limited (flow limited) b. Drug --- slow diffusion -----membrane cell : permeability rate limited (diffusion) Redistribution

Highly lipid soluble drugs when given by i.v. or by inhalation initially get distributed to organs with high blood flow, e.g. brain, heart, kidney etc.

Later, less vascular but more bulky tissues (muscles,fat) take up the drug and plasma concentration falls and drug is withdrawn from these sites.

If the site of action of the drug was in one of the highly perfused organs, redistribution results in termination of the drug action.

Greater the lipid solubility of the drug, faster is its redistribution.

ionconcentratPlasmaDose

=Vd Volume of Distribution • Volume of Distribution (Vd) [ml or l]: = Amount of drug in the body [mg] / drug concentration plasma [mg/ml] • Volume of Distribution (Vd): apparent volume of body water that drug appears to distribute

into to produce a drug concentration equal to that in the blood. • Apparent and hypothetical volume in which the drug is dispersed. • Vd is an apparent volume (volume that the drug must be distributed in to produce measured

plasma concentration • Drug with near complete restriction to plasma compartment would have Vd = plasma volume

(.04 L/kg) = 2.8 L/70 kg patient • But: Many drugs are highly tissue bound => large Vd e.g. Chloroquine: Vd = 13,000 L

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Distribution

• Membrane permeability – cross membranes to site of action

• Plasma protein binding – bound drugs do not cross membranes – malnutrition = ®albumin = ⟨ free drug

• Lipophilicity of drug – lipophilic drugs accumulate in adipose tissue

• Volume of distribution Factors affecting the equilibrium distribution of drugs across the compartments

1. Membrane-impermeant drugs will be excluded from the intracellular volume (Example: Lithium)

2. Lipophilic drugs will be enriched in the fat tissue (example: Thiopental – see later) 3. Drugs with a high degree of protein binding will be more concentrated in the plasma (the

intravascular volume) than in the interstitial fluid • To be absorbed and distributed, drugs must cross barriers (membranes) to enter and leave the

blood stream. Body contains two type of barriers which are made up of epithelial or endothelial cells: A. External (Absorption Barriers): Keratinized epithelium (skin), ciliated epithelium (lung), epithelium with microvilli (intestine) These epithelial cells are connected via zonulae occludens (tight junctions) to create an

unbroken phospholipid bilayer. Therefore, drugs MUST cross the lipophilic membrane to enter the body (except parenteral) B. Internal (Blood-Tissue Barriers): Drug permeation occurs mostly in the capillary bed, which is made up of endothelial cells

joined via zonulae occludens. Blood-Tissue Barrier is developed differently in various capillary beds:

1. Cardiac muscle: high endo- and transcytotic activity-> drug transport via vesicles 2. Endocrine glands, gut: Fenestrations of endothelial cells (=pores closed by diaphragms)

allow for the passage of small molecules. 3. Liver: Large fenestration (100 nm) without diaphragms-> drugs exchange freely between

blood and interstitium 4. CNS, placenta: Endothelia lack pores and possess only little trans-cytotic activity-> drugs

must diffuse transcellularly, which requires specific physicochemical properties -> Barriers are very restrictive, permeable only to certain types of drugs.

• Plasma: 4 liters. • Interstitial volume: 10 liters. • Intracelullar volume: 28 liters • Plasma compartment

(*) Vd: around 5 L. (*) Very high molecular weight drugs, ordrugs that bind to plasma proteins excesively Example: heparin 4L (3-5)

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• Extracellular fluid (*) Vd: between 4 and 14 L. (*) Drugs that have a low molecular weight but are hydrophilic. Example : Atracuronium 11 L (8-15) Do not cited this article without permittion from Ms. Farida

Vd equal or higher than total body water

• Diffusion to intracelullar fluid . Vd equal to total body water. – Ethanol 38 L (34-41) – Alfentanyl 56 L (35-77)

• Drug that binds strongly to tissues. Vd higher than total body water. – Fentanyl: 280 L – Propofol: 560 L – Digoxin:385 L

Key factor in the onset of drug action-Body Water Compartments • BODY WATER COMPARTMENTS: 50Kg & 100Kg ---- (110 lb) (220 lb) • Total body water (60% body weight) = 0.6 L/Kg, 30 L & 60 L • Extracellular (20% body weight) = 0.2L/Kg, 10 L & 20 L • Plasma (4% body weight) = 0.04L/Kg, 2 L & 4 L • Interstitial (16% body weight) = 0.16L/Kg, 8 L & 16 L • Intracellular (40% body weight) = 0.4 L/Kg, 20 L & 40 L • Drugs which bind selectively to Plasma proteins e.g. Warfarin have Apparent volume of

distribution smaller than their Real volume of distribution. • The Vd of such drugs lies between blood volume and total body water i.e. b/w 6 to 42 liters. • Drugs which bind selectively to Extravascular Tissues e.g. Chloroquine have Apparent volume

of distribution larger than their Real volume of distribution. • The Vd of such drugs is always greater than 42 liters. Body fluids

water sources (water drinking/water contained in food/metabolism to CO2 & H2O) water losses (urinary loss, fecal loss, insensible H2O loss, sweat loss, pathological loss) electrolytes (electrolyte losses: renal excretion, stol losses, sweating, abnormal routes

(vomit & diarrhea) Differences In Drug Distribution Among Various Tissues Arises Due To a Number of Factors:

Tissue Permeability of the Drug a. Physiochemical Properties of the drug like Molecular size, pKa and o/w Partition coefficient. b. Physiological Barriers to Diffusion of Drugs.

Organ / Tissue Size and Perfusion Rate Binding of Drugs to Tissue Components (Blood components, Extravascular Tissue Proteins) Miscellaneous Factors (Age, Pregnancy, Obesity, Diet, Disease states, and Drug Interactions)

• Tissue Permeability of the Drugs depend upon:

1. Rate of Tissue Permeability, and 2. Rate of Blood Perfusion.

• The Rate of Tissue Permeability, depends upon Physiochemical Properties of the drug as well as Physiological Barriers that restrict the diffusion of drug into tissues.

• Physiochemical Properties that influence drug distribution are: i. Molecular size,

ii. pKa, and iii. o/w Partition coefficient.

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Drugs having molecular wt. less than 400 daltons easily cross the Capillary Membrane to

diffuse into the Extracellular Interstitial Fluids. Now, the penetration of drug from the Extracellular fluid (ECF) is a function of :- Molecular Size:

Small ions of size < 50 daltons enter the cell through Aq. filled channels where as larger size ions are restricted unless a specialized transport system exists for them.

Ionisation: A drug that remains unionized at pH values of blood and ECF can permeate the cells more

rapidly. Blood and ECF pH normally remains constant at 7.4, unless altered in conditions like Systemic

alkalosis/acidosis. PENETRATION OF DRUGS THROUGH BLOOD BRAIN BARRIER • A stealth of endothelial cells lining the capillaries. • It has tight junctions and lack large intra cellular pores. • Further, neural tissue covers the capillaries. • Together , they constitute the BLOOD BRAIN BARRIER. • Astrocytes : Special cells / elements of supporting tissue are found at the base of endothelial

membrane. • The blood-brain barrier (BBB) is a separation of circulating blood and cerebrospinal fluid

(CSF) maintained by the choroid plexus in the central nervous system (CNS).

Since BBB is a lipoidal barrier • It allows only the drugs having high o/w partition coefficient to diffuse passively where

as moderately lipid soluble and partially ionized molecules penetrate at a slow rate. • Endothelial cells restrict the diffusion of microscopic objects (e.g. bacteria ) and large or

hydrophillic molecules into the CSF, while allowing the diffusion of small hydrophobic molecules (O2, CO2, hormones).

• Cells of the barrier actively transport metabolic products such as glucose across the barrier with specific proteins.

Various approaches to promote crossing BBB: • Use of Permeation enhancers such as Dimethyl Sulfoxide. • Osmotic disruption of the BBB by infusing internal carotid artery with Mannitol. • Use of Dihydropyridine Redox system as drug carriers to the brain ( the lipid soluble

dihydropyridine is linked as a carrier to the polar drug to form a prodrug that rapidly crosses the BBB )

PENETRATION OF DRUGS THROUGH PLACENTAL BARRIER • Placenta is the membrane separating Fetal blood from the Maternal blood. • It is made up of Fetal Trophoblast Basement Membrane and the Endothelium. • Mean thickness in early pregnancy is (25 µ) which reduces to (2 µ) at full term. • Many drugs having mol. wt. < 1000 Daltons and moderate to high lipid solubility e.g. ethanol,

sulfonamides, barbiturates, steroids, anticonvulsants and some antibiotics cross the barrier by simple diffusion quite rapidly .

• Nutrients essential for fetal growth are transported by carrier mediated processes.

12Do not cited this article without permittion from Ms. Farida

Blood – Cerebrospinal Fluid Barrier:

The Cerebrospinal Fluid (CSF) is formed mainly by the Choroid Plexus of lateral, third and fourth ventricles.

The choroidal cells are joined to each other by tight junctions forming the Blood – CSF barrier which has permeability characteristics similar to that of BBB.

Only high lipid soluble drugs can cross the Blood – CSF barrier. Blood – Testis Barrier:

It has tight junctions between the neighboring cells of sertoli which restricts the passage of drugs to spermatocytes and spermatids.

Organ / Tissue Size and Perfusion Rate

Perfusion Rate is defined as the volume of blood that flows per unit time per unit volume of the tissue.

Greater the blood flow, faster the distribution. Highly perfused tissues such as lungs, kidneys, liver, heart and brain are rapidly equilibrated with lipid soluble drugs.

The extent to which a drug is distributed in a particular tissue or organ depends upon the size of the tissue i.e. tissue volume.

Miscellaneous Factors • Diet: A Diet high in fats will increase the free fatty acid levels in circulation thereby affecting

binding of acidic drugs such as NSAIDS to Albumin. • Obesity: In Obese persons, high adipose tissue content can take up a large fraction of lipophilic

drugs. • Pregnancy: During pregnancy the growth of the uterus, placenta and fetus increases the volume

available for distribution of drugs. • Disease States: Altered albumin or drug – binding protein conc. • Altered or Reduced perfusion to organs /tissues • Altered Tissue pH WHAT ARE THE DETERMINANTS OF WHERE DRUGS GO? Determinants of Drug Distribution:

• Organ blood flow • Barriers to drug diffusion • Adipose tissue • Tissue protein binding • Plasma protein binding • Drug transport • Ion trapping

WHAT IS THE EFFECT OF ORGAN BLOOD FLOW ON DRUG DISTRIBUTION? • Organs with high blood flow will have larger amounts of drug delivered to them per unit time. • Organs with high blood flow will experience initial high concentrations of drug, but these high

concentrations will diminish as the drug is redistributed throughout the body to sites with lower blood flow.

• Organs with high blood flow will experience larger initial effects. • Many sedative/hypnotics, such as benzodiazepines (e.g., diazepam,[Valium®]) will produce initial, but short-lived, profound CNS effects

following IV administration.


WHAT IS THE EFFECT OF BARRIERS TO DRUG DIFFUSION ON DRUG

DISTRIBUTION? • Most capillaries have pores between the endothelial cells lining the capillaries. • These pores allow for rapid diffusion of most drugs into the interstitial space. • In some capillary beds, however, the endothelial cells are closely connected by “tight

junctions”, and such capillaries do not have pores between the endothelial cells. WHAT IS THE EFFECT OF BARRIERS TO DRUG DIFFUSION ON DRUG DISTRIBUTION? • In capillaries with tight junctions, drug molecules must diffuse across (transcellular), rather than

around (paracellular) the endothelial cells. • Only lipophilic drugs rapidly diffuse across capillary beds with tight junctions, whereas

hydrophilic drugs are mostly excluded. WHAT IS THE EFFECT OF BARRIERS TO DRUG DIFFUSION ON DRUG DISTRIBUTION? The “blood-brain barrier (BBB)” is a special case: • Capillaries in brain have tight junctions that contribute to the BBB. • Capillaries in brain are wrapped by pericapillary glial cells that further contribute to the BBB. • The endothelial cells in brain capillaries have P-glycoprotein that pumps drugs out of

endothelial cells, and this also contributes to the BBB. • In general, the BBB restricts the movement of hydrophilic drugs into brain; however, the BBB

is “broken” by ischemia and inflammation. • The BBB can be exploited to develop drugs with reduced CNS adverse effects. WHAT IS THE EFFECT OF ADIPOSE TISSUE ON DRUG DISTRIBUTION? • Lipophilic drugs will distribute into adipose (fat) tissue. • Distribution of lipophilic drugs into fat may necessitate a larger initial bolus of drug to achieve

the desired effect. • Large depots of drug in fat may necessitate a longer period of time for drug to be removed

from the body. • The distribution of lipophilic drugs will be different in thin versus obese patients.

WHAT IS THE EFFECT OF TISSUE PROTEIN BINDING ON DRUG DISTRIBUTION? • Some drugs are highly bound to tissue proteins. • Binding of drugs by tissue may necessitate a larger initial bolus of drug to achieve the desired

effect. • Large depots of drug in tissue may necessitate a longer period of time for drug to be removed

from the body. WHAT IS THE EFFECT OF PLASMA PROTEIN BINDING ON DRUG DISTRIBUTION? • Some drugs are highly bound (> 90%) to plasma proteins. • Acid drugs bind to albumin and basic drugs bind to alpha1-acid glycoprotein. • Binding of drugs by plasma proteins limits the distribution of drugs out of the vascular

compartment, necessitating more drug initially to achieve the desired effect. • Binding of drugs may limit the delivery of drugs to drug elimination mechanisms (for example

excretion by the kidney or metabolism by the liver), and this increases the time required for the drug to be removed from the body.


WHAT IS THE EFFECT OF PLASMA PROTEIN BINDING ON DRUG DISTRIBUTION?

• Displacement of a highly plasma-protein bound drug by another drug may lead to drug-drug interactions because of a rapid increase in the availability of “free” (unbound) drug.

• Displacement of unconjugated bilirubin from albumin by drugs may precipitate bilirubin encephalopathy in newborns.

WHAT IS THE EFFECT OF DRUG TRANSPORT ON DRUG DISTRIBUTION? • Transport mechanisms may increase or decrease the distribution of drugs to certain tissues.

For example, most diuretics are transported by the proximal tubules into the nephron, a process that delivers the diuretics to their site of action.

• Competition for transport may result in drug-drug interactions. For example, probenecid ( a drug used for gout) blocks the transport of diuretics into the

proximal tubule and thereby markedly blunts the effects of diuretics on salt and water excretion.

WHAT IS THE EFFECT OF I0N TRAPPING ON DRUG DISTRIBUTION? • Ion trapping can be used to distribute drugs into the urinary compartment to increase the urinary

excretion of poisons. • Example: Alkalinization of the urine with systemic administration of sodium bicarbonate is

useful for the treatment of overdoses of aspirin and phenobarbital. • Example: Acidification of the urine with systemic administration of ammonium chloride is

useful for the treatment of amphetamine overdoses.



DOSEN : Farida Lanawati Darsono,S.Si.,M.Sc Topic 3 : Drug Accumulation in Lysosom Steps in lysomal formation

1. The ER and Golgi apparatus make a lysosome 2. The lysosome fuses with a digestive vacuole 3. Activated acid 4. hydrolases digest the contents

Early endosome : pH 6.5-6 and sorting endosome Late endosome : pH 5.5-5 Lysosome : pH 5-4.5

• Lysosomes are vesicles produced by the Golgi aparatus. • Lysosomes contain hydrolytic enzymes and are involved in intracellular digestion. • Protein rich membranes (Lamp/Limp family of glycoproteins) • Unusual lipids

1. lyso-bisphosphatidic acid 2. thought to protect lysosomal membrane lipids from action of lumenal lipases

• Multivesicular bodies (late endosomes/lysosomes) 1. invagination of the limiting membrane 2. forms internal membranes

TM proteins can segregate into limiting or internal membranes limiting membrane can be recycled, internal is not

• Lysosomes receive cellular and endocytosed proteins and lipids that need digesting. • The metabolites that result are transported either by vesicles or directly across the membrane Ion trapping: lysosomes • Lysosomes are membrane-enclosed organelles • Contain a range of hydrolytic enzymes responsible for autophagic and heterophagic digestion • Abundant in Lung, Liver, kidney, spleen with smaller quantities in brain, muscle • pH maintained at ~5 (4.8).

Passive process: BH+ ====base ====Bun === BH+ ---- lysosome (acidic) equilibrium : [Bun] inside = [Bun] outside [BH+] inside > [BH+] outside result : acumulation

pH & pka : A- ===HA ====HA ====A- ---- lysosome equilibrium : [A-] outside >[A-] inside result : no acumulation

16


Weak base ---- ion trapping ------- accumulation (Vd >>>) BH+ ====BH+ ====B === BH+ ---- BH+ dibasic/ion trapping

Lipophilic cationic drugs increase the permeability of lysosomal membranes in a cell culture system • Lysosomes accumulate many drugs several fold higher compared to their extracellular

concentration. • This mechanism is believed to be responsible for many pharmacological effects. • So far, uptake and release kinetics are largely unknown and interactions between

concomitantly administered drugs often provoke mutual interference. In this study, we addressed these questions in a cell culture model.

• The molecular mechanism for lysosomal uptake kinetics was analyzed by live cell fluorescence microscopy in SY5Y cells using four drugs (amantadine, amitriptyline, cinnarizine, flavoxate) with different physicochemical properties.

• Drugs with higher lipophilicity accumulated more extensively within lysosomes, whereas a higher pKa value was associated with a more rapid uptake.

• The drug-induced displacement of LysoTracker was neither caused by elevation of intra-lysosomal pH, nor by increased lysosomal volume.

• We extended our previously developed numerical single cell model by introducing a dynamic feedback mechanism.

• The experimental data and results from the numerical model lead to the conclusion that intra-lysosomal accumulation of lipophilic xenobiotics enhances lysosomal membrane permeability. Manipulation of lysosomal membrane permeability might be useful to overcome, for example, multi-drug resistance by altering subcellular drug distribution

(Journal of Cellular Physiology, Volume 224, Issue 1, pages 152–164, July 2010)

Accumulation of Drugs in Tissues • Drugs need to achieve an adequate concentration in their target tissues in order to exert

pharmacological action. • The concentration of a drug at any moment and in any region of the body depends on

translocation of the drug molecules and the chemical transformations they undergo due to metabolic action.

• This article focuses on movement of drug molecules across cell barriers, absorption, distribution, and various approaches for drug delivery

(Pharmaceutical Sciences Encyclopedia: Drug Discovery, Development, and Manufacturing, Published Online: 15 MAR 2010,DOI: 10.1002/9780470571224.pse043) The role of lysosomes in the cellular distribution of thioridazine and potential drug interactions • The purpose of the present study was to investigate the contribution of lysosomal trapping to the total

tissue uptake of thioridazine and to potential drug distribution interactions between thioridazine and tricyclic antidepressants (imipramine, amitriptyline) or selective serotonin reuptake inhibitors (SSRIs; fluoxetine, sertraline).

• The experiment was carried out on slices of various rat tissues as a system with intact lysosomes. • The results show that the contribution of lysosomal trapping to the total tissue uptake of thioridazine is

as important as phospholipid binding.

17 Do not cited this article without permittion from Ms. Farida

http://onlinelibrary.wiley.com/doi/10.1002/jcp.v224:1/issuetoc




• A high degree of dependence of thioridazine tissue uptake on the lysosomal trapping is the cause of

substantial distributive interactions between thioridazine and the investigated antidepressants at the level of cellular distribution.

• Thioridazine and the antidepressants, both tricyclic and SSRIs, mutually decreased their tissue uptake.

Intracellular Distribution-based Anticancer Drug Targeting: Exploiting a Lysosomal Acidification Defect Associated with Cancer Cells • The potency of antidepressants to decrease thioridazine uptake was similar to that of lysosomal

inhibitors. • In general, the observed interactions between thioridazine and antidepressants occurred only in

those tissues in which thioridazine showed lysosomotropism (the lungs, liver, kidneys, brain, and muscles) but were not observed in the presence of ammonium chloride.

• The above finding provides evidence that the interactions proceeded at the level of lysosomal trapping.

• In the adipose tissue and heart no lysosomal trapping of thioridazine was detected and those tissues were not the site of such an interaction.

• Since the organs and tissues involved in the distributive interactions constitute a major part of the organism and take up most of the total drug in the body, the interactions occurring in them may cause a substantial shift of the drugs to organs and tissues poor in lysosomes, e.g. the heart and muscles.

(Toxicology and applied pharmacology ISSN 0041-008X CODEN TXAPA9, 1999, vol. 158, no2, pp. 115-124 (1 p.1/4) , Elsevier, Amsterdam, PAYS-BAS (1959) (Revue)) nano-polymer • the pH is slightly depressed in early to mid stage endosomes even before material is delivered to

the lysosome. • There are a number of materials that can respond to changes in acidity, for example simple

polymers with pendant carboxyl groups. • At hight pH, above the polymer's pKa, the carboxyl groups are all ionised. • The chain as a whole has a large negative charge, which repels neighbouring chains, but attracts

water molecules which hydrogen bond into the structure. • As the pH is lowered, the proton concentration increases. • At some critical pH - equivalent to the polymer's pKa, the carboxyl groups are protonated, and

loose their charge. • The polymer chain become a lot less hydrophilic, and has a tendency to stick to itself, adopting a

clumped up or globular conformation, (http://www.nanofolio.org/research/paper08.php) Intracellular Distribution-based Anticancer Drug Targeting: Exploiting a Lysosomal Acidification Defect Associated with Cancer Cells • The therapeutic usefulness of anticancer agents relies on their ability to exert maximal toxicity

to cancer cells and minimal toxicity to normal cells. • The difference between these two parameters defines the therapeutic index of the agent. • Towards this end, much research has focused on the design of anticancer agents that have

optimized potency against a variety of cancer cell types; however, much less effort is spent on the design of drugs that are minimally toxic to normal cells.

• We have previously described a concept for a novel drug delivery platform that relies on the propensity of drugs with optimal physicochemical properties to distribute differently in normal versus cancer cells due to differences in intracellular pH gradients.


http://www.refdoc.fr/?traduire=en&FormRechercher=submit&FormRechercher_Txt_Recherche_name_attr=listeTitreSerie:%20(Toxicology%20and%20applied%20pharmacology)

http://www.refdoc.fr/?traduire=en&FormRechercher=submit&FormRechercher_Txt_Recherche_name_attr=identifiantsDoc:%20(0041-008X)

http://www.nanofolio.org/research/paper08.php

• Specifically, we demonstrated in vitro that certain weakly basic anticancer agents had the

propensity to distribute to intracellular locations in normal cells that prevent interaction with the drug target, and to intracellular locations in cancer cells that promote drug-target interactions. We refer to this concept broadly as intracellular distribution-based drug targeting.

• Here we will discuss current in vivo work from our laboratory that examined the role of lysosome pH on the intracellular distribution and toxicity of inhibitors of the Hsp90 molecular chaperone in mice.

(Molecular and Cellular Pharmacology, Vol 2, No 4 (2010)) Lysosomes Contribute to Anomalous Pharmacokinetic Behavior of Melanocortin-4 Receptor Agonists • Weakly basic drugs with optimal physicochemical properties can be extensively sequestered

into lysosomes according to a pH-partitioning type mechanism. • When administered orally in animals, this particular sequestration event can manifest itself in

long term retention in the liver and negligible levels in blood. • This work revealed the mechanism for liver retention and provided a rational platform for the

design of a new analog with decreased liver accumulation and better opportunity for pharmacokinetic analysis and therapeutic activity.

(Pharmaceutical Research, Volume 24, Number 6, 1138-1144, DOI: 10.1007/s11095-007-92) Do not cited this article without permittion from Ms. Farida

19

http://www.springerlink.com/content/0724-8741/

http://www.springerlink.com/content/0724-8741/24/6/


DOSEN : Farida Lanawati Darsono,S.Si.,M.Sc Topic 4 : Drug Protein Binding Ikatan O-P • Merupakan suatu ikatan yg terbentuk dari hasil interaksi obat dg protein di dalam plasma • Merupakan suatu ikatan yg menghasilkan kompleks makromolekul Sifat ikatan O-P a. Reversibel: * ikatan kinia yg lemah (ikt. Hidrogen/gaya van der waals) * contoh : gol asam amino --- penyusun rantai protein b. Irreversibel: * ikatan kimia yg kuay (ikt. Kovalen) * timbul toksisitas * contoh : a. jangka pendek : parasetamol --- hepatotoksisitas b. jangka panjang : parasetamol – karsinogenik kimia • Protein binding generally refers to the binding of a drug to proteins in blood plasma. • The interaction can also be between the drug and tissue membranes, red blood cells, and other

components of the blood. • The amount of drug bound to protein determines how effective the drug is in the body. • The bound drug is kept in the blood stream while the unbound components of the drug may be

metabolized or extracted, making them the active part of the drug. So, if a drug is 95% bound to a binding protein and 5% is free, that means that 5% of the drug is active in the system and causing pharmacological effects.

• Protein binding is often reversible and thus creates a chemical equilibrium, in which the chemical reaction can go backward and forward with no net change in reactants and products.

• This means that a cell that is effective at extracting the unbound drug may extract more of the drug as it disassociates in the course of achieving equilibrium.

• The equation for reversible protein binding is: Protein + drug ⇌ Protein-drug complex • The proteins commonly involved with protein binding are albumin, lipoproteins, and al-

glycoprotein. • A protein is a chain of amino acids joined by peptide bonds. • Acidic drugs will tend to bind to albumin, which is basic and basic drugs will primarily bind to

al-glycoprotein, which is acidic. • Acidic drugs may also bind to lipoproteins if the albumin is saturated. Lipoprotein binding is

not binding in the strict sense of the term; it is closer to dissolving and is common in lipid soluble drugs.

• A drug that binds to tissue often binds to melanin-rich tissue or DNA. • The amount of protein binding and the fraction unbound, written as the concentration of

unbound drug over the total concentration of the drug, depends on several factors. • It is determined by the drug’s affinity for the protein, the concentration of the binding protein,

and the concentration of the drug relative to the binding protein. • This is important when considering other medications that a patient might be on because certain

proteins may already be saturated, which would affect the amount of free drug and possibly change the desired pharmacologic effects.


http://www.wisegeek.com/what-is-plasma.htm

http://www.wisegeek.com/what-is-a-chemical.htm

http://www.wisegeek.com/what-is-albumin.htm

http://www.wisegeek.com/what-are-amino-acids.htm

http://www.wisegeek.com/what-is-a-peptide.htm

http://www.wisegeek.com/what-is-a-lipoprotein.htm

http://www.wisegeek.com/what-is-melanin.htm

http://www.wisegeek.com/what-is-dna.htm

• For example, if drug A saturated a certain binding protein and then drug B was not able to bind

to that protein, then there would be a higher concentration of unbound drug B. Drug B could also competitively displace drug A from the binding protein, thus raising the unbound fraction of drug A.

• This process happens fairly quickly, in minutes to hours, and both scenarios could have adverse effects. Many drugs, however, have different binding proteins, different binding sites on a protein, or are not present in high enough relative concentration to saturate the proteins, and so do not compete with the other drug or drugs in use.

• Likewise, the ability of the body to extract the drug can affect the drug’s clearance into the body.

• Renal failure and liver disease often negatively impact the body’s ability to extract the unbound drug.

• For these reasons, it is important to consider previous medical issues, the total concentration of the drug, the unbound fraction of the drug, and any other medications a patient may be taking.

• So, if a drug is 95% bound to a binding protein and 5% is free, that means that 5% of the drug is active in the system and causing pharmacological effects.

• Protein binding is often reversible and thus creates a chemical equilibrium, in which the chemical reaction can go backward and forward with no net change in reactants and products.

• In addition to being a unique structure, a bacterial protein also has the ability to bind with other proteins.

• Protein binding involves the formation of very strong links between two different proteins. (http://www.wisegeek.com/what-is-protein-binding.htm) Membrane Proteins • An enzyme called protein kinase C is another interior peripheral membrane protein. • It initiates signaling pathways inside the cell. • Peripheral membrane proteins do not interact with the non-polar region of the cell

membrane. • Both structurally and functionally, they are integral parts of the membranes of cells. • Each integral membrane protein molecule has an intricate relationship with the membrane

within which it is situated. • Various routes are used to administer drugs but in most cases drugs reach their site of action via

the systemic circulation. • Once within the circulation a drug is clearly not confined to its intended site of action. • Instead it is distributed widely throughout the body. • At this point you may have anticipated some important questions: • How is the drug carried in the blood? Is the entire drug free to exert an effect? • Can the presence of one drug in the circulation affect another? • To begin to understand the answer to these questions we need first of all to think about plasma

proteins (http://www.nottingham.ac.uk/nmp/sonet/rlos/bioproc/plasma_proteins/6.html)

21


http://www.wisegeek.com/what-is-renal-failure.htm

http://www.wisegeek.com/what-are-the-different-types-of-liver-disease.htm

Plasma Proteins • Suppose we take a sample of blood and mix it in a tube with an anticoagulant to stop it clotting,

before spinning it in a centrifuge. What now will our sample look like? • The cellular components will have sunk to the bottom of the tube – they form about 45% of the

sample. • The remaining 55% is the liquid we call plasma. What does plasma consist of? • Most of it is water – about 92%, whilst plasma proteins form about 7%. • The remaining 1% is other dissolved solutes such as inorganic ions. Types of Plasma Protein • Most, but not all, plasma proteins are manufactured in the liver including albumins. • These are the most abundant and form about 60% of all plasma proteins. • They contribute to osmotic pressure, help to control water balance and are involved in the

transport of substances in blood including drugs. • Globulins (globular proteins) form 35% of the whole and include antibodies, whilst others have

transport functions. • Approximately 4% of plasma proteins, such as fibrinogen, have a clotting function whilst the

remaining less than 1% are regulatory such as metabolic enzymes Drugs and Plasma Proteins • The main influence of plasma proteins on drugs is in their distribution. • The most important plasma proteins in this context are albumin, acid-glycoprotein and beta-

globulin. • Once a drug has been absorbed into the circulation it may become attached (we say bound) to

plasma proteins. • However this binding is rapidly reversible and non-specific – that is many drugs may bind to

the same protein. • It is important to recognise that plasma proteins do not represent target tissues and drug binding

produces no physiological effect. • Drug–plasma protein binding forms a "reservoir" of drug, but only the free (unbound) drug is

available to the tissues to exert a therapeutic Jenis protein yg terikat dg obat

Albumin α1-acid glycoprotein (AAGP) lipoprotein

albumin • Disintesi di hati • BM= 65.000-69.000 • Terdistribusi di plasma dan cairan ekstraseluler • T ½ eliminasi = 17-18 hari • Konsentrasi normal : 3,5 – 5,5 % atau 4,5 mg/dL • Fungsi :

1. mengatur tekanan osmotis darah 2. trasnpor komponen endogenous dan exogenous (ex: free fatty acid, bilirubin, hormon)


22

• Bersifat selektif • Terdiri dari 6 tempat ikatan

* 2 --- mengikat kuat --- asam lemah * 2 --- mengikat bilirubin * 1 --- mengikat obat (site 1) * 1 --- mengikat obat (site 2)

• Memiliki pH = (-) ve charge • Mengikat obat yg bersifat asam lemah • Low binding afinity & high binding capacity AAGP • Is an acute phase reaction which has one binding site selective for basic drug • BM = 44.000 • Konsentrasi dalam plasma = 0,4 – 1% • Terutama mengikat obat yg bersifat basa (kationik) • Level konsentrasi AAGP akan mengikat pada kondisi: a. trauma b. kehamilan c. myocardial infraction d. chronic RF e. malignancy lipoprotein • Merupakan komplek makromolekul antara lemak dg protein • Berdasarkan “density” dan “pemisahan secara ultrasentrifuse” terdiri dari:

1. VLDL 2. LDL 3. HDL --- good protein

• Berfungsi transpor lemak plasma dan ikatan obat (jika albumin jenuh) --- siklosporin, trigliserida, kolesterol

• Memiliki “non polar lipid core” : 1. ester kolesterol & trigliserida 2. fosfolipid & free kolesterol 3. apo-lipoprotein

• Binds (terikat) highly with lipoprotein drug • Lipoprotein level changes depend on fasted or fed state • Competition binding with albumin RBCs (Red Blood Cells) • Mengikat kedua komponen endogenous & exogenous • Meliputi 45 % dr volume darah • Tidak terlalu berpengaruh pada Vd


23

Cara evaluasi OP

Tujuan : untuk mengetahui sejauh mana ikatan obat dengan protein yg terjadi Umumnya secara : in vitro Perangkat yg diperlukan :

a. instrumen b. protein yg dimurnikan ---albumin c. membran semipermiabel

Metode penentuan : a. langsung : uv-vis, NMR, dll b. dialisis : ultracentrifugation

Keuntungan : pengukuran lebih mudah, hemat waktu, peralatan umum Kerugian : biaya mahal

Faktor yg mempengaruhi OP 1. Obat : * Sifat fisikokimia * [C] total dalam tubuh 2. Afinitas obat terhadap protein: * tetapan asosiasi (ka) 3. Interaksi obat: * kompetisi : obat vs zat lain * perubahan protein (sbg substrat) 4. Patofisiologis pasien: * kelainan liver atau ginjal, dll 5. Protein Factor affecting drug protein binding 1. factor relating to the drug

a) Physicochemical characteristic of drug b) Concentration of drug in the body c) Affinity of drug for a particular componant

2. factor relating to the protein and other binding componant a) Physicochemical characteristic of the protein or binding componant b) Concentration of protein or binding componant c) Num. Of binding site on the binding site

3. drug interation 4. patient related factor

Drug related factor

Physicochemical characteristics of drug Protein binding is directly related to lipophilicity

lipophilicity = the extent of binding e.g. The slow absorption of cloxacilin in compression to ampicillin after i.m. Injection is

attributes to its higher lipophilicity it binding 95% letter binding 20% to protein Highly lipophilic thiopental tend to lacalized in adipose tissue . Anionic or acidic drug like . Penicillin , sulfonamide bind more to HSA Cationic or basic drug like . Imepramine alprenolol bind to AAG

24


CONCENTRATION OF DRUG IN THE BODY

The extent of drug- protein binding can change with both change in drug and protein concentration

The con. of drug that binding HSA does not have much of an influence as the thereuptic concentration of any drug is insufficient to saturate it

Eg. Thereuptic concentration of lidocaine can saturate AAG with which it binding as the con. Of AAG is much less in compression to that of HSA in blood DRUG PROTEIN / TISSUE AFFINITY

Lidocaine have greater affinity for AAG than HSA Digoxin have greater affinity for protein of cardiac muscle than skeleton muscles or plasma

Protein or tissue related factor Physicochemical properity of protein / binding componant – lipoprotein or adipose tissue tend to bind lipophilic drug by dissolving them to lipid core . The physiological pH determine the presence of anionic or cationic group on the albumin molecule to bind a verity of drug Concentration of protein / binding componant Mostly all drug bind to albumin b/c it present a higher concentration than other protein Number of binding sites on the protein Albumin has a large number of binding site as compare to other protein and is a high capacity binding component Drug interaction a. Competition b/w drug for binding site (displacement interaction ) When two or more drug present to the same site , competition b/w them for interaction with

same binding site . If one of the drug (A) is bound to such a site , then administration of the another drug (B) having high affinity for same binding site result in displacement of drugs (A) from its binding site. This type of interaction is known as displacement interaction. Wher drug (A) here is called as the displaced drug and drug (B) as the displacer .

Eg. Phenylbutazone displace warferin and sulfonamide fron its binding site b. Competition b/w drug and normal body constituent

The free fatty acids are interact to with a number of drug that bind primarily to HSA . When free fatty acid level is increase in several condition – fasting , - pathologic – diabeties , myocardial infraction , alcohol abstinence – the fatty acid which also bind to albumin influence binding of several drug binding – diazepam - propanolol binding - warferin

Acidic drug like – sod. Salicilate , sod . Benzoate , sulfonamide displace bilirubin from its albumin binding site result in neonate it cross to BBB and precipitate toxicity (kernicterus )


25

Disease state

Disase Influence on plasma protein

Influence on protein drug binding

Renal failure (uremia)

albumin content

Decrease binding of acidic drug , neutral or basic drug are

unaffected Hepatic failure

albumin synthesis

Decrease binding of acidic drug ,binding of basic drug is

normal or reduced depending on AAG level.

Inflammatory state (trauma , burn, infection )

AAG levels

Increase binding of basic drug , neutral and acidic drug

unaffected

Hal-hal yg harus diperhatikan dalam evaluasi OP • Kondisi setimbang antara obat terikat & obat bebas dapat dipertahankan • Metode yg dipakai harus valid untuk rentang konsentrasi yg cukup besar • Kontaminasi & denaturasi protein yg akan dipakai tidak terjadi • Metode yg dipakai harus mempertimbangkan : pH, [C] ionik dr media, donan efek • Metode tsb dapat mendeteksi ikatan OP yg bersifat reversibel dan irreversibel • Hasil mencerminkan kondisi :”in vivo”

Kinetics of protein drug binding

Hukum : Aksi Massa Reaksi :

The kinetics of reversible drug–protein binding for a protein with one simple binding site can be described by the law of mass action, as follows:

(persamaan 1)

The law of mass action, an association constant, K a, can be expressed as the ratio of the molar concentration of the products and the molar concentration of the reactants. This equation assumes only one-binding site per protein molecule

(persamaan 2)

26


Experimentally, both the free drug [D] and the pro ein-bound drug [PD], as well as the total protein

r=tetapan yg m

moles of drug bound is [PD] and the total moles of protein is [P] + [PD], this equation becomes

(persamaan 3) Substituting the value of

(persamaan 4)

This equation describes the simplest situation, in which 1 mole of drug binds to 1 mole of protein in

(persamaan 5) In terms of K d, which is 1/

(persamaan 6) Protein molecules are qu ntain more than one type

(persamaan 7)

t

concentration [P] + [PD], may be determined. To study the binding behavior of drugs, a determinable ratio (r )is defined, as follows

enunjukkan perilaku ikatan OP

PD from equa. 2

a 1:1 complex. This case assumes only one independent binding site for each molecule of drug. If there are n identical independent binding sites per protein molecule, then the following is used:

K a, Equation 6 reduces to

27

ite large compared to drug molecules and may coof binding site for the drug. If there is more than one type of binding site and the drug binds independently on each binding site with its own association constant, then Equation 6 expands to


28

The values for the association constants and the number of binding sites are obtained by various graphic methods.

ikatan dan tempat ikatan dg metode grafik Metode in vivo

. Direct plot It is made by plotting r vresus (D)

Advantages: using direct data Disadvantages: difficult to reach a saturated condition

. graphic method = double reciprocal plot= klotz plot

sadvantages: non-linier 1/[D] vs 1/r

dv ed for multiple binding sites – non linier isadvantages: variability >

Penetapan tetapan•• Metode in vitro

1

[D] vs r

2

Equation : (see ppt)

Ad Di

vantages: data bias 3. scatchard plot Equation : (see ppt)

r/[D] = nka - rka

r vs r/[D]

A antages: can be usD


29

. rosenthall method

Equation : [DP]/[D] = nka[P] total – ka[DP]

sites – non linier Disadvantages: variability >

dengan obat terikat protein

a : • Suatu komplek yang besar

ara bebas

terapeutik

INGINKAN DALAM PENGGUNAAN OBAT nyakit

Hilangkan gejala penyakit

DIINGINKAN :

Efektoksik

MPING OBAT fek ikutan yang muncul setelah pemberian obat dengan dosis sesuai anjuran

Efek samping : tidak dikehendaki, merugikan, membahayakan pasien sisten dan sudah diketahui

4 Advantages: can be used for multiple binding 5. Langmuir method

Equation : (see ppt)

] vs [D]/r

[D

Perbedaan antara obat bebas Obat terikat protein plasm

• Tidak dapat lewat membran sel • Distribusi terbatas Do not cited this article without permittion from Ms. Farida • Tidak aktif secara terapeutikObat bebas : • Dapat lewat membran sel sec• Distribusi luas • Aktif secara EFEK YANG DI• Hilangkan penyebab pe• • Terapi untuk gantikan /menambah zat yang hilang/kurang EFEK OBAT YANG TIDAK• Efek samping • • Alergi • Teratogenik EFEK SA• Pengertian : e• • Efek samping bersifat kon


30

Significant of protein binding of drug • Absorption –the binding of absorbed drug to plasma proteins decrease free drug conc. And

disturb equilibrium . Thus sink condition and conc. Gradient are established which now act as n

e

for such drug hydrophobic compound .

Tis onfined to blood have small volume of

distribution. f distribution .

the driving force for further absorptio• Systemic solubility of drug water insoluble drugs , neutral endogenous macromolecules , lik

heparin , steroids , and oil soluble vitamin are circulated and distributed to tissue by binding especially to lipoprotein act as a barrier

• Distribution -The plasma protein-drug binding thus favors uniform distribution of drug throughout the body by its buffer function . A protein bound drug in particular does not crossthe BBB, placental barrier and the glomerulus

sue binding , apperent volume of distribution and drug storage A drug that bind to blood component remains c

Drug that show extra-vascular tissue binding have large volume o the relationship b/w tissue drug binding and apparent volume of distribution

Vd = amount of drug in the body = X plasma drug concentration C the amount of drug in the body X = Vd . C

Amount of drug in extravascular tissue = Vt .Ct

d . C = Vp.C+Vt. Ct

here , Vp is volume of plasma travascular tissue

t is tissue drug concentration

Dividing both side by C in above equation

a

SIMILAR , amount of drug in plasma = Vp . S The total amount of drug in the body V w Vt is volume of ex C Vd = Vp + Vt Ct/C ………………….(1)

The fraction of unbound drug in plasma (fu) fu = conc. of unbound drug in plasm = Cu

C total plasma drug concentration The fraction unbound drug in tissue (fut) fut = Cut Ct

unbound or free drug conc. In plasma and tissue is equal Assuming that equilibrium C t = fu C fut Do not cited this article without permittion from Ms. Farida

31

ean Cu = Cut then , m Vd = Vp + Vt . fu

t

n eqution above in plasma larger its Vd

• For a drug showing little protein binding, the plasma acts simply as a watery solution in which the drug is dissolved.

of the drug may be influenced in several

otein binding will increase the amount of drug that has to be absorbed

h as acetyl salicylic acid – aspirin) are often substantially bound to albumin.

• d

• A utrition. It may also be caused by

renal failure where there is excessive excretion of albumin. In each case the result is a

•

•

t of free drug. which displaces

fu substituting the above value iIt is clear that greater the unbound or free concentration of drug What is the effect of protein binding on drug action?

• Where protein binding does occur the behaviour ways: 1. Extensive plasma pr

before effective therapeutic levels of unbound drug are reached. For example, acidic dugs (suc

2. Elimination of a highly bound drug may be delayed. Since the concentration of free drug is low, drug elimination by metabolism and excretion may be delayed. This effect is responsible for prolonging the effect of the drug digoxin

Changes in the concentration of plasma proteins will influence the effect of a highly bound rug. low plasma protein level may occur in old age or maln

illness such as liver disease (remember that most plasma proteins are made in the liver), or chronicsmaller proportion of drug in bound form and more free drug in the plasma. The greater amount of free drug is able to produce a greater therapeutic effect and reduced drug dosages may be indicated in these cases. Drugs may compete for binding with plasma proteins leading to interactions.

• This is significant for highly bound drugs such as the anticoagulant warfarin since even a small change in binding will greatly affect the amoun

• Such an effect is produced by the concurrent administration of aspirin, warfarin and increases the amount of free anticoagulant


32


Topic 5 : Pharmacokinetic Linier and Non Linier

DOSEN : Farida Lanawati Darsono,S.Si.,M.Sc

bjectives: ted with nonlinear pharmacokinetic

To understand the effect of parallel pathways eters Km and Vm

ed, that the concentration at steady state will increase proportionately,

old, the plasma drug concentration will

than

g

what causes non-linear pharmacokinetic behaviour?

clearance of the drug.

s.

s clearance, volume of distribution, and half life, may vary depending on the

t expected to change when different tion or

•

• on-time curve (AUQ will be increased proportionally

n

nonlinear pharmacokinetics of

• elimination) may be via a process other than simp

• , different doses of these drugs may not result in parallel plasma concentration-

OTo understand the schemes and differential equations associamodels • • To estimate the param• To design appropriate dosage regimen for drugs with nonlinear elimination introduction what is meant by non-linear pharmacokinetics? • when the dose of a drug is increas• we expect i.e. if the dose rate is increased or decreased say two-f

also increase or decrease two-fold. •

• However, for some drugs, the plasma drug concentration changes either more or lesswould be expected from a change in dose rate.

• This is known as non-linear pharmacokinetic behaviour and can cause problems when adjustindoses.

it was shown that the steady state blood concentration (Css) is a function of both the dose and the

Differentiation between Linear and Nonlinear Kinetic• For these drugs (drugs with nonlinear kinetics or dose-dependent kinetics), the kinetic

parameters, such aadministered dose.

• The pharmacokinetic parameters of most drugs are nodoses are administered or when the drug is given through different routes of administraas single or multiple doses. The kinetics (e.g. cle arance and volume of distribution) of these drugs are said to be linear or dose-independent, and this is a characteristic of first-order kinetics. The term linear simply means that if the dose is increased, the plasma concentration or area under the plasma concentrati

• However, for some drugs, this may not be valid. For example, when the dose of phenytoin is increased by 50 percent i• n a patient from 300 mg/day to 450 mg/day, the average steady state concentration may increase by as much as tefold.

• This dramatic increase in the concentration is due to the phenytoin. This is because one or more of the kinetic processes of the drug (absorption, distribution, and/or le first-order kinetics. For these drugs, the relationship between the AUC or CSS and dose is not linear Additionallytime courses expected for drugs with linear pharmacokinetics.


33

For example, for drugs with nonlinear metabolism, the initial decline in the plasma

concentrations may be slower at higher doses, compared with that after the administration of the lower doses

This means that the rate of elimination is not directly proportional to the plasma concentration

Sources of Nonlinearity.

Adistribution, and/or elimination.

For distribution, plasma protein binding of disopyramide is saturable at therapeutic g in an increase in the volume of distribution with an increase in dose

• on, it has been shown that the antibacterial agent enal

• ism, both phenytoin and ethanol have saturable metabolism which means an

• h is one of the most common sources of

Ca aturable metabolism

• olism of drugs may be explained by the relationship depicted First, the drug interacts with the enzyme to produce a drug-enzyme intermediate.

a metabolite and release the

ism (v)

• his relationship, at very low drug concentrations, the concentration of available

s

.

further, there will be no change in the rate of metabolism of the drug

•

•for these drugs.

• s mentioned above, nonlinearity may be at different kinetic levels of absorption,

•concentrations, resultinof the drug As for nonlinearity in renal excretidicloxacillin has saturable active secretion in the kidneys, resulting in a decrease in rclearance with an increase in dose For metabolincrease in the dose would result in a decrease in hepatic clearance and a more thanproportionate increase in the drug AUC. Here, nonlinearity in the metabolism, whicnonlinearity, will be discussed.

pacity-limited metabolism is also called s• Michaelis-Menten kinetics, or mixed-order kinetics.

The process of enzymatic metab•• Then, the intermediate complex is further processed to produce

enzyme. • The released enzyme is recycled back to react with more drug molecules • According to the principles of Michaelis-Menten kinetics, the rate of drug metabol

changes as a function of drug concentration as demonstrated. Based on tenzymes is much larger than the number of drug molecules.

• Therefore, when the concentration of the drug is increased, the rate of metabolism is increased almost proportionally (linearly).

• However, after certain points, as the concentration increases the rate of metabolism increaseless than proportional.

• The other extreme occurs when the concentration of the drug is very high relative to theconcentration of available enzyme molecules

• Under this condition, all of the enzymes are saturated with the drug molecules, and when the concentration is increased

• In other words, the maximum rate of metabolism (V^sub max^) has been achieved


34

Proses non-linier pada tahap ADM Absorpsi:

* transpor dalam dinding usus --- jenuh (riboflavin) * tidak larut (griseofulvin)

motilitas --- perubahan efek farmakologi (metoklopramida)

* saturasi enzaim/keterbatasan ko-faktor (fenitoin,

l)

tabolit (diazepam)

an OP (asam salisilat) * efek nefrotoksik (aminoglikosida)

engikuti order satu ditingkatkan

AUC tidak sebanding dg dosis an enzim/carrier yg sama

obat atas dasar dosis yg kecil

Asam p-aminobenzoat ----asetilasi

S• tukan suatu obat mengikuti kinetika non linier • (*) obat iberikan pada berbagai tingkat dosis

suatu kurva konsentrasi pbat dalam plasma vs waktu untuk tiap dosis

E

•

* saturasi :fist past effect” (salisilamid, propanolol) * perubahan * kejenuhan peruraian di lambung (penicilin) • Distribusi :

* saturasi ikatan OP (salisilat) * kejenuhan transpor (metotreksat) • Metabolisme / non renal:

asam salisilat) * induksi enzim (karbamazepin) * hepatotoksik (parasetamo * perubahan aliran darah hepatik (propanolol) * penghambat me• Ekskresi / renal:

* sekresi aktif (penisilin G) * reabsorpsi aktif ( asam askorbat) * perubahan pH urin, kejenuhan ikat

* efek diuretik (teofilin) Karakteristik atau fenomena kinetika non-linier • Eliminasi obat ~ non linier ~ tidak m• T ½ eliminasi > bila dosis •• Eliminasi fipengaruhi obat yg lain yg memerluk• Komposisi metabolit dipengaruhi oleh dosis Kesulitan FNL : memprakirakan konsentrasi Obat-obat yg mengalami proses metabolisme terbatas/penjenuhan • Salisilat -----konjugasi glisin • Salisilamid ---konjugasi sulfat •• Fenitoin ---eliminasi Contoh proses yg dapat jenuh :

• Biotransformasi • Sekresi tubular aktif ginjal

tudi FNL Tujuan : untuk menenCara :

(*) dibuat (*) slop sejajar atau tidak


35

Eliminasi non linier • Kinetika Michaelis Menten • Laju eliminasi = -dC/dt = {(Vm x Cp)/(Km + Cp)}

um haelis Menten

atu Km --- eliminasi order nol

• Concentration or dose dependent kinetics

sociated with metabolism may be saturable mum rate limited by substrate tion to parmacokinetics

M R Km+Cp

here Vm is the maximum rate of metabolism and Km is Michaelis constant, the concentration rate is ½ maximum

quation at Low Concentration

dCp/dt =- Vm•Cp /Km =- k'•Cp

rst order elimination

quation at High Concentration

p > Km

dCp / dt = - Vm•Cp/Cp =- Vm

der elimination

dimana : Vm = laju eliminasi maksim Km = tetapan Mic• Jika Cp << Km --- eliminasi order s• Jika Cp >> Nonlinear Processes • Lower concentration > first order • Higher concentration > zero order

• Enzyme reaction as• Enzyme reaction may have a maxi• Basic enzyme kinetics have applica

ichaelis-Menten Kinetics

ate of Elimination = Vm•Cp w(or amount) of drug at which the E Km > Cp Km + Cp » Km Therefore pseudo fi E C Km + Cp » Cp Therefore zero or


36

tion Slope constant on linear graph == zero order Slope approaches

r

/2

t1 a ation Dc /dt =-kel x C =- Vm x C/Km+ C

/2 = 0.693 x (Km+ C)/Vm

Km/t) x ln(Co/Ct)}

t = {1/Vm x (Co/Ct)} + (Km x ln(Co/Ct)}

ubungan Cp dan Vm terhadap waktu dalam penentuan dosis

Vm = 100 mg/jam ---- t1 = 4,93 jam Vm = 200 mg/jam ---- t2 = 2,46 jam

(Km : tinggi --- Vm : konstan---t ½ eliminasi : naik)

kondisi jenuh

2. Metode B

R2 = { (Vm x C2)/(Km+ C12}

High Dose - Concentra

-Vm Low Dose - Concentration

• Slope constant on semi-log graph == first orde• Slope approaches -Vm/Km

Effect of MM Kinetics on t1/2 l rger as concentration increases; i.e. slower elimin

since kel = 0.693/t1/2 0.693 / t1/2 = Vm / Km+ C t1 Persamaan

{Co – Ct/t} = {Vm-{(

{Do – Dt/t} = {Vm-{(Km/t) x ln(Do/Dt)} t = {1/Vm x (Do/Dt)} + (Km x ln(Do/Dt)}

H D0 = 400 mg --------Dt = 20 mg

(Vm : tinggi --- Km : konstan---t ½ eliminasi : turun)

D0 = 400 mg --------Dt = 20 mg Km = 38 mg/jam ---- t1 = 2,46 jam Km = 76 mg/jam ---- t2 = 3,03 jam

Metode penentuan Km dan Vm pada1. Metode A Css = {(Vm x Css) / R} + (1/Vm)

R = {-Km x (R/Css)} + (Vm) 3. Metode C R = { (Vm x Css)/(Km+ Css)} 4. Metode D R1 = { (Vm x C1)/(Km+ C1)}


37

etode penentuan Km dan Vm pada kondisi tanpa penjenuhan * Metode 1

1/V = { (Km/Vm) x 1/C)} + (1/Vm) * Metode 2

an oleh ikatan OP : eliminasi ---- lebih panjang

c. bila Cp ----- fb

Satura anisms causes a change in intrinsic clearance Drug m• The metabolism of drugs is carried out by a variety of enzymes such as cytochromeP450 and N-

acetyltransferase. The dependence of the rate of an enzyme reaction on substrate concentration

ncentrations, the maximal rate of metabolism is reached and cannot be

•

of the drug in the body is eliminated per unit time.

viduals, theophylline.

Exa

• A• Therapeutic window 10 - 20 mg/L (total Cp)

ose adjustment is not appropriate greater than 24 hr at higher doses

mg/L when t1/2 is 12 hr)

ons in the therapeutic

Consequently, small increases in dose result in large increases in total and unbound y state drug concentration.

oncentrations at doses of 300, 360 and 400 mg/day would be 10.0,

e required to achieve phenytoin concentrations in the

M

C/V = { (1/Vm) x C)} + (Km/Vm) * Metode 3

V = - {Kmx (V/C)} + Km/Vm

Farmakokinetika yang disebabk a. t ½ b. filtrasi glomerulus

tion of elimination mechetabolism

is given by the Michaelis-Menten equation • At high drug co

exceeded. Under these conditions, a constant amount of drug is eliminated per unit time no matter how much drug is in the body.

• Zero order kinetics then apply rather than the usual first order kinetics where a constantproportion

• Some examples of drugs which exhibit non-linear kinetic behaviour are phenytoin, ethanol, salicylate and, in some indi

mple - Phenytoin

• Average Km » 4 mg/L (1 - 15 mg/L) verage Vm = 500 mg/day (100 - 1000 mg/day)

• Overdose possible if d• Half-life at low doses » 12 hr, maybe • From 25 to 23 mg/L in 24 hours (cf. 25 > 12.5 > 6 Phenytoin:

Phenytoin exhibits marked saturation of metabolism at concentratirange (10-20 mg/L)

stead As an example, for a patient with typical Km of 5 mg/L (total drug) and Vmax of 450

mg/day, steady state c20.0 and 40.0 mg/L respectively (Fig. 2). Thus, small dosage adjustments artherapeutic range of 10-20 mg/L.


38

second consequence is that, because clearance decreases, apparent half-life increases from about 2 hours at low phenytoin concentrations to as long as a week or more at high concentrations.

his means that

. in the therapeutic range, the phenytoin concentration fluctuates little over a 24 hour period daily dosing and sampling for drug concentration monitoring at any time between

iii centrations in the toxic range, phenytoin concentration initially falls

Al

• tions in the range of pharmacological effect are well above the Km.

max for ethanol metabolism is about 10 g/hour (12.8 mL/hour) and it can be calculated f 0.05 g%, the rate of alcohol

• ght beer, 236 mL standard beer, 88 mL wine or

•

• In Article 7 (`Clearance of drugs by the kidneys' Aust Prescr 1992;15:16-9), it was shown that r arance minus reabsorption.

lomerular filtration is a passive process which is not saturable, but secretion

• a drug

ds ration in the drug's elimination.

mportant problems.

Saly

blood. For drugs with high hepatic extraction ratios, e.g. alprenolol, an increased dose can result in

olism are tropisetron and paroxetine.

A1 Ti. the time to reach steady state can be as long as 1-3 weeks at phenytoin concentrations near the

top of the therapeutic range ii

allowing once doses

. if dosing is stopped with convery slowly and there may be little change over a number of days.

cohol: • Alcohol is an interesting example of saturable metabolism.

The Km for alcohol is about 0.01 g% (100 mg/L) so that concentra

• The V(see legend to Fig. 2) that at the common legal driving limit ometabolism per hour is 8.3 g/hour. This amount of alcohol is contained in 530 mL li27 mL spirit. Higher rates of ingestion will result in further accumulation.

Renal excretion

enal drug clearance is the sum of filtration clearance plus secretion cle

• Clearance by ginvolves saturable drug binding to a carrier. Even when secretion is saturated, filtration continues to increase linearly with plasmconcentration.

• The extent to which saturation of renal secretion results in non-linear pharmacokinetics depenon the relative importance of secretion and filt

• Because of the baseline of filtration clearance, saturation of renal secretion does not usually cause clinically i

turation of first pass metabolism causing an increase in bioavailability

• After oral administration, the drug-metabolising enzymes in the liver are exposed to relativehigh drug concentrations in the portal

•saturation of the metabolising enzymes and an increase in bioavailability (F).

• Steady state drug concentration then increases more than proportionately with dose (equation 3). Other drugs with saturable first pass metab


39

aturation of protein binding sites causing a change in fraction of drug unbound In plasma In a few cases (e.g. salicylate, phenylbutazone, diflunisal), therapeutic drug concentrations are

high enough to start to saturate albumin binding sites so that unbound protein concentration decreases and fu increases while total drug concentration increases less than proportionately

S•

with increases in dose • This occurs more commonly for drugs such as disopyramide which bind to a1 acid

glycoprotein because of the lower concentration of binding protein.


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