Pharmacology and Clinical Toxicology: Mechanisms, Interactions, and Antidotes
Pharmacology questions combine mechanism of action with clinical consequences: indications, adverse effects, interactions, and overdose management. Build a framework around pharmacokinetics (absorption, distribution, metabolism, excretion) and pharmacodynamics (receptors, dose–response).
Concepts to master
- Pharmacokinetics: half-life, volume of distribution, clearance, first-pass metabolism, and loading vs. maintenance doses.
- Key mechanisms: beta-blockers, ACE inhibitors, diuretics, anticoagulants, antibiotics, and their adverse effects.
- Drug interactions: CYP450 induction/inhibition, protein binding, and additive toxicity.
- Toxicology: toxidromes (opioid, anticholinergic, cholinergic, sympathomimetic) and specific antidotes.
- Special populations: renal and hepatic dosing, pregnancy, and pediatrics.
Traps
Questions often present a classic adverse effect disguised as a new disease (e.g., ACE inhibitor cough, statin myopathy). Another trap is choosing an antidote without confirming the toxidrome. Be careful with half-life questions: steady state takes about 4–5 half-lives, and loading doses depend on volume of distribution, not clearance. Watch for interactions that are theoretically possible but clinically minor.
Worked rule of thumb
For any overdose: stabilize ABCs, identify the toxidrome, then match the antidote (opioid → naloxone; benzodiazepine → flumazenil only with caution; acetaminophen → N-acetylcysteine; organophosphate → atropine plus pralidoxime; methanol/ethylene glycol → fomepizole). For dosing, use half-life to estimate time to steady state and volume of distribution to estimate loading dose.