Pharmacology and Pharmacotherapeutics
Core concepts
Master receptor pharmacology (agonists, partial agonists, antagonists, inverse agonists), dose–response relationships, potency versus efficacy, and therapeutic index. Know pharmacokinetics: absorption, distribution (protein binding, volume of distribution), metabolism (phase I/II, CYP450, induction/inhibition), excretion, and the equations - clearance, half-life, steady state (4–5 half-lives), loading dose. Understand pharmacodynamics of major drug classes: antihypertensives (ACE inhibitors, ARBs, CCBs, diuretics), antidiabetics, antibiotics (mechanism and resistance), anticoagulants, analgesics, and psychotropics. Recognise adverse effects, contraindications, and clinically important interactions.
Traps
Distinguish potency (dose needed) from efficacy (maximal effect). Half-life changes with clearance and volume of distribution - a larger Vd lengthens half-life. Enzyme inducers (rifampicin, carbamazepine, phenytoin) lower drug levels; inhibitors (ketoconazole, erythromycin, grapefruit) raise them. First-order versus zero-order kinetics: alcohol and phenytoin saturate. Watch for prodrugs requiring activation (e.g., clopidogrel via CYP2C19).
Worked example
Loading dose = (Vd × target concentration) / bioavailability. If Vd = 50 L, target = 2 mg/L, F = 1, loading dose = 100 mg. Maintenance dose = clearance × target concentration × dosing interval / F - a common calculation trap is forgetting to convert units or include F.
Exam strategy
For each drug, recall mechanism → therapeutic use → key adverse effect → major interaction. This four-part grid answers most questions.