Pharmacology and therapeutics: mechanisms, monitoring and individual variation
Mechanisms, monitoring and individual variation
Pharmacology and therapeutics questions test whether you can link a drug’s mechanism to its clinical effects, adverse effects and monitoring. Know receptor types and signalling, agonist/partial agonist/inverse agonist/antagonist behaviour, potency versus efficacy, and therapeutic index. Potency is the concentration or dose producing a given effect (often EC50); efficacy is the maximal response. A competitive antagonist shifts the agonist concentration–response curve right without reducing Emax; a non-competitive or irreversible antagonist can reduce Emax. Therapeutic index is a safety margin, not a guarantee; drugs with narrow indices need therapeutic drug monitoring and careful dose titration.
Therapeutics requires matching treatment to the patient, not just the diagnosis: age, pregnancy/lactation, renal and hepatic function, comorbidities, interacting medicines, adherence and patient preference. Understand common mechanisms of adverse drug reactions, dose-related versus idiosyncratic reactions, and clinically important CYP induction/inhibition and transporter interactions. Antimicrobials illustrate selective toxicity, spectrum, resistance and stewardship. Analgesics illustrate multimodal analgesia and opioid safety.
Traps: choosing the most potent drug as “best”; assuming all agonists are full agonists; ignoring active metabolites and renal clearance; applying adult doses to children or frail older people; and confusing prophylaxis with treatment.
Worked rule: for a competitive antagonist, first ask whether Emax changes (usually no) and whether EC50 rises (yes). For any therapeutic choice, use the sequence: indication → contraindications → interactions → organ function → monitoring → counselling. “Start low, go slow” is a useful rule in older adults and renal impairment, but it does not replace calculation or guideline-based dosing.