Pharmacology

Pharmacokinetics, autonomic drugs, toxicities and antidotes — reason from receptor to side effect rather than memorising lists.

Exam weight 11–15% · 2 QBank items · 3 flashcards

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Pharmacokinetics

Volume of distribution = amount in body / plasma concentration; high Vd means tissue-bound drug that dialysis cannot remove.
Loading dose = Cp × Vd / F and is unchanged in renal failure; maintenance dose = Cp × CL / F and must be reduced.
Zero-order elimination: phenytoin, ethanol, aspirin at high dose ('PEA').
Weak acids (aspirin) are trapped and excreted with urinary alkalinisation; weak bases with acidification.

β1 increases heart rate and contractility and renin; β2 causes bronchodilation, vasodilation and uterine relaxation.
α1 vasoconstriction and mydriasis; α2 decreases central sympathetic outflow (clonidine, α-methyldopa).
Organophosphate poisoning: DUMBBELSS — treat with atropine plus pralidoxime.
Nonselective β-blockade masks hypoglycemia symptoms and worsens Prinzmetal angina and cocaine-induced vasospasm.

Acetaminophen → N-acetylcysteine; opioids → naloxone; benzodiazepines → flumazenil (risks seizures).
Warfarin → vitamin K plus 4-factor PCC; heparin → protamine sulfate; dabigatran → idarucizumab.
Methanol/ethylene glycol → fomepizole; carbon monoxide → 100% or hyperbaric oxygen; cyanide → hydroxocobalamin.
Lead → EDTA, dimercaprol, succimer; iron → deferoxamine; copper (Wilson) → penicillamine or trientine.

CYP inducers ('chronic alcoholics steal phen-phen and never refuse greasy carbs'): carbamazepine, phenytoin, phenobarbital, rifampin, griseofulvin, St John's wort.
CYP inhibitors: cimetidine, ketoconazole, macrolides (not azithromycin), grapefruit juice, ritonavir, isoniazid.
Sulfa allergy cross-reactivity: sulfonamides, sulfonylureas, thiazides, furosemide, celecoxib.
QT prolongers: class IA and III antiarrhythmics, macrolides, antipsychotics, ondansetron, methadone — risk of torsades.