Pharmacology, Pharmacotherapeutics and Clinical Pharmacy
This domain integrates pharmacology, therapeutics and clinical pharmacy: receptor mechanisms, pharmacokinetics, drug selection, interactions, adverse drug reactions, monitoring and patient counselling.
Core principles
- Pharmacodynamics: agonist/antagonist, potency versus efficacy, therapeutic index.
- Pharmacokinetics: absorption, distribution, metabolism (CYP450), excretion; half-life, clearance and volume of distribution; renal and hepatic dose adjustment.
- Therapeutics: choose by indication, contraindication, comorbidity, pregnancy/lactation, interactions, cost and adherence.
- Clinical pharmacy: medication history, reconciliation, therapeutic drug monitoring, ADR causality (for example Naranjo), counselling and pharmacovigilance.
Worked example
A patient stabilised on warfarin develops an infection and is prescribed fluconazole. Reasoning: fluconazole inhibits CYP2C9, reducing warfarin metabolism; INR rises and bleeding risk increases. Check INR within a few days, consider a non-interacting antifungal or reduce the warfarin dose, and counsel on bleeding signs. This is a pharmacokinetic interaction, not a pharmacodynamic one.
Traps
Calling every interaction contraindicated; confusing inhibitors (azole antifungals, macrolides) with inducers (rifampicin, carbamazepine); adjusting only for creatinine without considering hepatic metabolism; attributing an ADR without a causality assessment; counselling on dose but not on administration timing, food or missed doses.