Pharmacology: Receptors, Pharmacokinetics, and Drug Classes
Core concepts
Pharmacology questions reward a systems approach: receptor type, signal transduction, and clinical consequence. Know G-protein-coupled receptors (Gs → ↑cAMP; Gi → ↓cAMP; Gq → ↑IP3/DAG), ligand-gated ion channels, tyrosine kinase receptors, and nuclear receptors. Link autonomic drugs to receptor selectivity: α1 vasoconstriction, β1 cardiac stimulation, β2 bronchodilation, M2 cardiac slowing, M3 secretion and smooth muscle contraction.
Pharmacokinetics
Master first-order elimination, half-life, volume of distribution, clearance, and steady state (≈4–5 half-lives). Loading dose = Vd × target concentration / bioavailability; maintenance dose = CL × target concentration / bioavailability. Zero-order (saturation) kinetics applies to phenytoin, ethanol, and high-dose aspirin. Know CYP inducers (rifampin, carbamazepine, phenytoin, St. John's wort) and inhibitors (ketoconazole, erythromycin, grapefruit, ritonavir).
Pharmacodynamics and safety
Understand potency vs efficacy, competitive vs noncompetitive antagonism, therapeutic index, and tolerance/tachyphylaxis. Know key adverse effects that appear in questions: ACE inhibitors-cough/angioedema; aminoglycosides-nephro/ototoxicity; statins-myopathy; NSAIDs-GI/renal; corticosteroids-hyperglycemia/osteoporosis.
Traps and rule of thumb
Questions often ask for the drug that is contraindicated in a condition (e.g., nonselective β-blockers in asthma; ACE inhibitors in pregnancy). Rule of thumb: if a drug's effect is reversed by increasing agonist concentration, it is competitive; if not, noncompetitive.