Pharmacology: Rational Drug Selection and Adverse Effects
Pharmacology questions in an emergency context focus on indication, mechanism, dose route and the adverse effect that matters at the bedside. Organise your knowledge by receptor or target, then by clinical use. Know the adrenergic agents used in resuscitation, including the receptor profile of adrenaline (alpha and beta agonism) and why it is used in anaphylaxis and cardiac arrest; know the antimuscarinic action of atropine in symptomatic bradycardia; and know the antiplatelet and anticoagulant mechanisms used in acute coronary syndromes and thromboembolism. For analgesia, understand the opioid receptor effects and the reversal agent naloxone, and for sedation understand the benzodiazepine and reversal agent flumazenil, with the caveat that reversal can precipitate seizures in dependent patients.
For toxicology, know the toxidromes and their antidotes: opioid, anticholinergic, cholinergic and sympathomimetic patterns; paracetamol with N-acetylcysteine; organophosphate with atropine and pralidoxime; and carbon monoxide with high-flow oxygen.
Traps include choosing a drug by class without checking the contraindication, and forgetting that a reversal agent may unmask the original toxicity.
Worked example
A patient presents with salivation, lacrimation, urination, diarrhoea, bronchospasm and bradycardia after pesticide exposure. The rule of thumb is to recognise the cholinergic toxidrome and treat with atropine titrated to drying of secretions, with pralidoxime to reactivate the enzyme. Titrate to clinical effect rather than to a fixed dose.