Pharmacology and Pharmacotherapeutics
Pharmacology and Pharmacotherapeutics tests drug action, pharmacokinetics, rational drug selection and evidence-based prescribing. Questions often require linking mechanism to adverse effects and adjusting therapy for patient factors.
Core rules
- Pharmacokinetics is ADME: absorption, distribution, metabolism and excretion. Clearance determines maintenance dose; volume of distribution determines loading dose.
- Pharmacodynamics involves receptors, agonist/antagonist activity, potency and efficacy. Therapeutic index separates effective from toxic exposure.
- Renal and hepatic function, age, pregnancy and drug interactions change risk. CYP inhibition can raise concentrations; induction can lower them.
- Antimicrobial stewardship and guideline-based selection reduce resistance and unnecessary exposure.
Worked example
A 70-year-old woman weighing 60 kg has serum creatinine 1.2 mg/dL. Cockcroft–Gault: CrCl = [(140 − 70) × 60]/(72 × 1.2) × 0.85 = 41.3 mL/min. For a renally cleared drug such as gentamicin, this moderate reduction requires dose or interval adjustment and monitoring, not simply the standard adult dose.
Traps
- Calculating CrCl without the female factor or with inconsistent units.
- Confusing half-life with duration of action.
- Selecting a drug by diagnosis alone while ignoring renal function, interactions or allergy.
- Assuming a loading dose is adjusted in renal impairment when it usually depends on volume of distribution.