Paper I — 2025 August (Supplementary) (2010 Scheme) — Q4
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Paper I
2025 August (Supplementary) (2010 Scheme) · 40 marks · 120 min
Question
Drug antagonism.
Q43 marksShort Notes
Answer
Drug antagonism occurs when the combined effect of two drugs is less than expected — one drug reduces or abolishes another’s action.
Types:
Physical antagonism — a physical property, not receptor interaction (e.g. activated charcoal adsorbing a poison).
Chemical antagonism — the drugs react chemically, neutralizing each other (e.g. protamine neutralizing heparin).
Physiological (functional) antagonism — two agonists at different receptors produce opposite effects on the same system (e.g. histamine and adrenaline on bronchial tone).
Receptor antagonism — one drug directly blocks the receptor the other needs: competitive (reversible, shifts the agonist curve rightward without lowering the maximum — e.g. naloxone versus morphine) or non-competitive (binds an allosteric site, lowers the achievable maximum regardless of agonist concentration).
Clinical relevance: the basis of most antidote therapy (naloxone in opioid overdose, atropine in organophosphate poisoning, protamine in heparin overdose).
