Pharmacology and Rational Drug Use
Pharmacology and Rational Drug Use tests pharmacokinetics, interactions, renal and hepatic dosing, antimicrobial stewardship, pregnancy safety, and prescribing quality. The exam often presents a drug-related problem rather than a straight fact.
Core rules
- Before prescribing: confirm indication, dose, route, duration, allergies, renal and liver function, pregnancy status, and interactions.
- Renal dosing: calculate creatinine clearance for narrow-therapeutic drugs; avoid NSAIDs and aminoglycosides when safer options exist.
- Interactions: warfarin is affected by antibiotics, NSAIDs, and liver enzyme changes; monitor INR.
- Antimicrobials: do not treat viral upper respiratory infection with antibiotics; choose narrow spectrum when culture results allow.
Worked example
An older patient with atrial fibrillation on warfarin receives trimethoprim for a urinary tract infection. Trimethoprim inhibits warfarin metabolism and can raise INR and bleeding risk. Choose another antibiotic if possible, or monitor INR closely and adjust the warfarin dose. Reasoning: the interaction is predictable; the safest prescription is the one that anticipates it.
Traps
- Prescribing antibiotics for a viral cold.
- Using NSAIDs in CKD or heart failure.
- Starting ACE inhibitors in pregnancy.
- Forgetting dose adjustment in low body weight or renal impairment.