Pharmacology and pharmacotherapy: mechanisms, indications, contraindications, and adverse effects
What the exam tests
This domain asks you to connect a drug’s mechanism to its clinical use, its contraindications, its adverse-effect profile, and its interactions. Expect questions on cardiovascular drugs, analgesics, antimicrobials, antidiabetics, and drugs used in respiratory and gastrointestinal practice.
Core rules
- Pharmacodynamics explains what the drug does at the target; pharmacokinetics explains absorption, distribution, metabolism, and elimination.
- Indications and contraindications must be matched to the individual patient: age, pregnancy, renal and hepatic function, allergy history, and comorbidity.
- Most clinically important interactions are pharmacodynamic additivity or CYP-mediated metabolic changes.
- Adverse effects should be described by mechanism where possible, not only by symptom.
- Special populations need dose adjustment or avoidance, especially in renal impairment and older adults.
Worked example
A patient stabilised on warfarin asks whether diclofenac is suitable for knee pain.
Reasoning: diclofenac is a non-selective NSAID. It inhibits platelet cyclo-oxygenase and damages the gastric mucosa, so it adds to warfarin’s bleeding risk pharmacodynamically; it may also displace warfarin from protein binding and, for some NSAIDs, inhibit CYP2C9. The combination should be avoided. Paracetamol is a safer first choice if appropriate, and the INR should be checked if any analgesic change is made. The answer must include monitoring, not just “do not combine”.
Traps that cost marks
- Recommending a beta-blocker in a patient with asthma without recognising bronchospasm risk.
- Calling an ACE-inhibitor cough an “allergy” and missing the need to switch class.
- Ignoring renal function when dosing antibiotics, metformin, or anticoagulants.
- Assuming all penicillins can be used in anyone with a vague “antibiotic allergy”.
- Describing an adverse effect without linking it to mechanism or management.
Exam focus
For each drug, rehearse one mechanism, one key indication, one absolute contraindication, one common adverse effect, and one interaction.