Pharmacology and Clinical Pharmacotherapy: Kinetics, Interactions, and Safety
What the candidate must understand
Pharmacology questions combine mechanism with clinical consequence. Know absorption, distribution, metabolism, and elimination; first-order versus zero-order kinetics; half-life and steady state; and the meaning of bioavailability and volume of distribution. Understand receptor agonism and antagonism, dose–response relationships, and the major classes used in cardiovascular, infectious, endocrine, psychiatric, and analgesic therapy. Clinical pharmacotherapy questions test drug selection by comorbidity, dose adjustment in renal or hepatic impairment, interactions, and monitoring parameters.
Traps that appear in questions
- Forgetting that zero-order drugs such as phenytoin and ethanol do not follow proportional kinetics.
- Adjusting a dose for renal impairment without checking whether the drug is renally cleared.
- Missing a clinically important interaction, such as enzyme induction reducing efficacy or inhibition raising toxicity.
- Choosing a drug that is contraindicated by a comorbidity named in the stem.
- Stopping a drug abruptly when withdrawal or rebound is likely.
Worked example: half-life
A drug has a half-life of 8 hours. After starting a maintenance dose, roughly four to five half-lives, about 32–40 hours, are needed to reach steady state. The rule of thumb: loading doses fill the volume of distribution quickly, while maintenance dosing determines the steady-state concentration; in renal impairment, extend the interval or reduce the dose according to the fraction cleared by the kidney.
Rule of thumb
Before selecting any drug, check four things: indication, contraindication by comorbidity, organ function, and interaction with the current medication list.