Pharmacology and Therapeutics: Mechanism, Safety, and Selection
Pharmacology questions reward mechanism-based reasoning. For each major drug class, know the target, the main indication, the key adverse effect, and the important contraindication. Antibiotics: beta-lactams inhibit cell wall synthesis and are safe in pregnancy; aminoglycosides are nephrotoxic and ototoxic; fluoroquinolones are avoided in children and pregnancy. Cardiovascular drugs: ACE inhibitors cause cough and hyperkalemia and are contraindicated in pregnancy; beta-blockers blunt tachycardia; statins lower LDL and are avoided in pregnancy.
Pharmacokinetics
Understand absorption, distribution, metabolism, and elimination. First-order kinetics means a constant fraction is eliminated per unit time; zero-order means a constant amount, leading to accumulation and toxicity (for example, phenytoin at high doses, or ethanol). Half-life determines dosing interval and time to steady state (about four to five half-lives).
Safety and prescribing
Know high-alert medications, dosing in renal and hepatic impairment, and drug interactions such as warfarin with many antibiotics. Therapeutic drug monitoring applies to drugs with narrow therapeutic indices.
Traps
Questions often ask for the most likely adverse effect rather than the mechanism, or present a contraindication disguised as a valid indication. Watch for pregnancy and pediatric cautions.
Rule of thumb
Before selecting a drug, ask three questions: does the mechanism fit the disease, is there a contraindication in this patient, and what toxicity must I monitor?