Department of Pharmacology1 Pharmacokinetics • General principles of the fate of the drug in the body • Overview of pharmacokinetic processess: Drug absorption, distribution, metabolism and elimination Jan Juřica Pharmacokinetics Occupation theory: The intensity of pharmacological response (E) is proportional to the conentration of reversible drug-receptor complex = Action of a drug requires presence of a certain concentration in the fluid bathing the target tissue. Pharmacokinetics deals with the processes of absorption, distribution, metabolism excretion of the drug And their relationship with their biological (pharmacological) effect „WHAT DOES ORGANISM DO WITH THE DRUG“ A D M E invasion elimination “ADME“ What does influence the movements of the drug in the body? physico-chemical properties lipophilic/hydrophilic properties, molecule structure, pKa, charge… AH  A- + H+ B + H+  BH+ permeation across the membranes lipophilic – difusion (passive) hydrophilic – through the pores active transport bonds of the drugs to: plasma proteins blood cells in the circulation tissue receptors perfusion of the tissues a) brain, heart, liver, kidney b) fat tissue A bound drug has no effect! Amount bound depends on: 1) free drug concentration 2) the protein (binding sites) concentration 3) affinity for binding sites % bound: __[bound drug]__________ x 100 [bound drug] + [free drug] ABSORPTION Absorption – permeation of the soluted drug into the body fluids from the site of administration – necessary for the general (systemic) effect Local effect – on the skin, mucous membranes… mouth, rectum, vagina - absorption is fault, can cause difficulties, adverse effects) (local aenesthetics, corticosteroids) Rate and extent of absorption are described by the parameters : C max - max. concentration of the drug in the plasma after single administration T max - time after administration, when is Cmax F - bioavailability (extent of absorption) Bioavailability • The fraction of the dose of a drug (F) that enters the general circulatory system, F= amt. of drug that reach systemic circul. Dose administered F = AUCp.o./AUCi.v. Area under curve (AUC) Is a measure of bioavailability F= AUCp.o. /AUCiv Bioavailability Extravascular route - 0-100% (resp. 0-1). Intravenous - 100% = 1 If F is 0-20% = 0-0,2 – not suitable route of administration (in spite of that fact, some drugs are administered, even if the F ˂ 2-5 %, such as SET, bisphosphonates). F = AUCpo/AUCiv (the same drug, same dose, same patient) Bioavailability • A concept for oral (extravascular) administration • Useful to compare two different drugs or different dosage forms of same drug • depends, in part, on rate of dissolution (which in turn is dependent on chemical structure, pH, partition coefficient, surface area of absorbing region, etc.) Also firstpass metabolism is a determining factor Influence of the various bioavailability on the plasmatic levels of the drug First pass effect, presysthemic elimination Other factors influencing the absorption gender, body weight, plasma volume, gastric amptying rate, age - pH, bile, enzyme levels and activity patophysiological state – liver disseases, inflammation simultaneously eaten meal – acceleration/decelaration chemical incompatibilities function of the GIT Distribution = permeation from the blood to the tissues and site of the action is dynamic process rate - depends on: bonds (with the plasmatic proteins…) permeation across the membrabes blood perfusion through the organ state - distribution equilibrium; the the proportion of the free (unbounded) fractions of the drug in the blood and in the tissues are the same Barriers – the distribution is limited blood-brain barrier („leaky areas“ – area postrema), penicilines X aminoglycosides placental barrier… Volume of Distribution Volume of distribution – apparent, hypotethical the proportion of the quantity of the drug and reached plasmatic concentration Vd = D/C – Vd is the apparent volume of distribution – C= Conc of drug in plasma at some time – D = Total quantity (dose) of drug in system Vd gives one as estimate of how well the drug is distributed. Value < 0.071 L/kg indicate the drug is mainly in the circulatory system. Values > 0.071 L/kg indicate the drug has gotten into specific tissues. Volumes of the water in human body ELIMINATION Biotransformation – metabolism Sites of biotransformation anywhere, where the enzymes are present: plasma, kidney, lungh GIT, brain, but especially liver Enzymatic • biodegradation • bioactivation (prodrug) enalapril-enalaprilate codein-morphine bromhexin - ambroxol 1. Phase : oxidation, hydrolysis Cytochrom P450, dehydrogenases 2. Phase : conjugation – metabolites are more soluble in the water Metabolite - effective („more / less / in other way“) - ineffective - toxic men plants insect funghi yeast bacteria molluscs animals CYP 450 CYP 2D6 30% CYP 1A2 2% CYP 2C9 10% other 3% CYP 3A4 55% CYP 3A4 CYP 2D6 CYP 2C9 CYP 1A2 other Genetic polymorphism Genetic polymorphism = the existence of several (At least two ) alleles for the gene from which At least part has a population frequency of at least 1 % • Pharmacogenetics focuses on the study of genetically conditioned variability in the response to a drug •Pharmacogenomics examines the relationship of drug effect on the level of the whole genome, respectively transcriptome Genetic polymorphism of biotransformation enzymes Polymorphism in the gene of N - acetyltransferase - Inactivation of drugs in the liver : slow x fast acetylators - Isoniazide , procainamide, hydralazine - Peripheral neuropathy (prevention - pyridoxine) Polymorphism of thiopurine S - methyltransferase - the metabolism of azathioprine - commercially available genetic test for determining the polymorphisms, prevention of serious adverse reactions INDUCERS of CYP 450 • dexamethason • phenobarbital • rifampicine • phenytoin • St. John`s Wort (Hypericum perforatum) • Ginkgo biloba INHIBITORS of CYP 450 • antidepressants (fluoxetine, fluvoxamine, paroxetine) • quinine, quinidine • chloramphenicol, erythromycin • ketoconazol, itraconazol • grapefruit juice 5mg tablet + grepfruit juice 5 mg tablet Phase I of biotransformation hydroxylation -CH2CH3 → -CH2CH2OH oxidation -CH2OH → -CHO → -COOH O-dealkylation -CH2OHCH2 → -CH2OH + -CHO N-dealkylation -N(CH3)2 → -NHCH3 + CH3OH N-oxidation -NH2 → -NHOH oxidative deamination -CH2CHCH3 → -CHCOCH3 + NH3 NH2 Other non-microsomal biotransformations • hydrolysis of esters in plasma (suxamethonium by cholinesterase) • dehydrogenation of alcoholic and aldehydic group in cytosol in the liver (ethanol) • MAO in mitochondria (tyramine, noradrenaline, dopamine, amines) • xanthinoxidase (6-merkaptopurine, uric acid) • enzymes with distinct function (tyrosine-hydroxylase, dopadecarboxylase, etc.) Phase II of biotransformation CONJUGATION Glucuronides -OH, -SH, -COOH, -CONH wih glucuronyl acid (UDP- GlcUAc) Sulphates: with -OH functional group Acetylates: acetyl CoA with NH2, -CONH2, s aminoacid- group with gluthathion with -halogen- or -nitrate functional groups, epoxides sulphates tubulární sekrece glomerulární filtrace konjugace s aminokyselinami glukuronidace acetylace porod 10 20 30 2 3 4 5 6 dny měsíce birth acetylation conjugation with glucuronic acid conjugation with aminoacids glomerular filtration tubular secretion days months Excretion Kidney (urine) tubular excretion x tubular reabsorption liver (bile) lungh (air) saliva, skin, hair, breast milk... Kidney • MW < 60.000 D (MW albumin = 68.000 D) • tubular secretion – organic acids • furosemid • thiazide diuretics • penicilins • glucuronides – organic bases • Morphine • Atropine • Histamine… • tubular reabsorption acidification acetazolamid (inhibitor of CA) ammonium chloride alcalization sodium bicarbonate Liver Billiar excretion, clearance. enterohepatic circulation ELIMINATION = biotransformation + excretion Kinetics of the first order = rate of elimination is descending with the descending concentration in the blood (linear kinetics) Kinetics of the zero order = rate of elimination is constant (nonlinear kinetics) First Order Kinetics Elimination (first order) Elimination constant ke = lnc1 – ln c2 / t2-t1 Half-life of the elimination – the drug is completely eliminated after 4-5 t 0,5 t 0,5 = ln2/ ke = 0,7/ ke clearance Volume of the blood in a defined region of the body that is cleared of a drug in a unit time ClTOT = D/AUC = ke Vd Clearance Cl • Volume of blood in a defined region of the body that is cleared of a drug in a unit time. • more useful concept in reality than kel since it takes into account blood flow rate • Clearance varies with body weight • Also varies with degree of protein binding PHARMACOKINETIC PARAMETERS PRIMARY Bioavailability (F) Volume of distribution (Vd) Clearance (Cl) SECONDARY elimination half-life (T1/2) elimination constant (Ke) AUC (area under the curve) Cumulative index Extraction ratio