Pharmacology and Toxicology: Action and Poisoning Management
Pharmacology and Toxicology tests drug action from receptor to patient: pharmacodynamics, pharmacokinetics, therapeutic decision-making, adverse effects, and poisoning management.
Core rules
- Receptors include ligand-gated channels, GPCRs, kinase-linked receptors, and nuclear receptors. Competitive antagonism shifts the dose-response curve right; noncompetitive antagonism lowers Emax.
- Pharmacokinetics: absorption, distribution (Vd), metabolism (CYP), and excretion. First-order elimination predominates, but ethanol, phenytoin, and high-dose salicylate can show zero-order behavior.
- Loading dose = Vd × target concentration / F; maintenance dose = CL × target concentration / F.
- Therapeutic index = TD50/ED50; narrow-index drugs need monitoring.
- Antidotes: acetaminophen-N-acetylcysteine; organophosphate-atropine plus pralidoxime; opioid-naloxone; methanol-fomepizole or ethanol; warfarin-vitamin K; heparin-protamine.
Worked example
A drug has Vd 40 L and oral bioavailability 0.80. Target plasma concentration is 20 mg/L. Loading dose = (40 L × 20 mg/L)/0.80 = 1,000 mg. If given IV (F = 1), the dose would be 800 mg. Check units and whether the target is total or free drug.
Traps
Confusing potency with efficacy; assuming every drug is first-order; forgetting F in oral dosing; extrapolating animal doses; giving flumazenil in a mixed overdose with seizure risk; missing delayed acetaminophen toxicity.