USMLE Step 1 Review/Pharmacology

Pharmacodynamic and pharmacokinetic processes, general principles. Pharmacokinetics The four stages of chemicals passing through the body Absorption - the process of the intake of the drug into the body Distribution - the process of the dispersion of the drug into the blood stream and tissues Metabolism - the process of the parent compounding into daughter metabolites Excretion - the process of eliminating the drug from the body Dosage intervals Zero order pharmacokinetics, the rate of reaction is independent of the concentration of the reactants: r = k Drugs following zero order pharmacokinetics; Mnemonic: 'Peas & WHEATS' (A Pea would look like a zero and denotes the order). Pea also stands for 'Pee'-ing out a constant amount as in zero order kinetics constant amount of the drug is eliminated per unit time. Rate of elimination is constant and does not depend on or vary with the drug intake or plasma concentration of the drug. Phenytoin, Phenylbutazone Warfarin Heparin Ethanol Aspirin Theophylline, Tolbutamide Salicylates Absorption Many abbreviations are used in writing administration routes and frequency: p.o.: by mouth IM: intramuscular injection SC: subcutaneous injection IV: intravenous PR: per rectum h.s.: at hour of sleep (bedtime) ac: before meals pc: after meals q: every, ie, q 8 h means every 8 hours q.d.: every day b.i.d.: twice/day t.i.d.: three times/day q.i.d.: four times/day q.o.d.: every other day Distribution The volume of distribution is given by the following equation: Metabolism Drugs undergoing complete first pass metabolism when taken orally: 'FILTHy' First pass metabolism Isoprenaline Lignocaine (Lidocaine) Testosterone Hydrocortisone Drugs metabolized by acetylation, acetylator polymorphism: Some individuals are slow acetylators and some are fast acetylators.The drugs metabolized by acetylation may become ineffective in fast acetylators and cause toxicity in slow acetylators. Mnemonic: 'SHIP' Sulfonamides including dapsone Hydralazine Isoniazid (INH) Procainamide Enzyme inducers: 'SCRAP Bar' Sulphonylureas Carbemazepine Rifampicin Alcohol Pheytoin Barbituates Enzyme inhibitors 'COMIC CASE' Cimetidine Omeprazole Metronidazole Isoniazid Chloramphenicol Ciprofloxacin Allopurinol Sulphonamides Erythromycin Elimination Three sites where drug excretion occurs: The kidneys, the liver and the lungs. Drug actions mechanisms of drug action, structure-activity relationships (including anticancer drugs) concentration- and dose-effect relationships, types of agonists and antagonists and their actions individual factors altering pharmacokinetics and pharmacodynamics mechanisms of drug adverse effects, overdosage, toxicology mechanisms of drug interactions regulatory issues signal transduction, including structure/function of all components of signal transduction pathway such as receptors, ligands cell cycle/cell cycle regulation