USMLE Step 1 Review/Pharmacology
Pharmacodynamic and pharmacokinetic processes, general principles.
Pharmacokinetics[edit | edit source]
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
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
- Theophylline, Tolbutamide
Absorption[edit | edit source]
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[edit | edit source]
The volume of distribution is given by the following equation:
Metabolism[edit | edit source]
Drugs undergoing complete first pass metabolism when taken orally: 'FILTHy'
- First pass metabolism
- Lignocaine (Lidocaine)
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
- Isoniazid (INH)
Enzyme inducers: 'SCRAP Bar'
Enzyme inhibitors 'COMIC CASE'
Elimination[edit | edit source]
Three sites where drug excretion occurs: The kidneys, the liver and the lungs.
Drug actions[edit | edit source]
- 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