Pharmacology and Toxicology
Pharmacology and Toxicology in NIPER JEE tests pharmacodynamics, pharmacokinetics, autonomic and CNS pharmacology, cardiovascular drugs, and toxicological principles.
Core rules and concepts
- Potency is the dose producing a given effect (EC50); efficacy is maximal response. A competitive antagonist shifts the agonist curve right with unchanged Emax; a noncompetitive antagonist reduces Emax.
- First-order elimination: t½ = 0.693/k. Vd = dose/C0 after IV bolus. Clearance = dose/AUC. Zero-order elimination gives a constant amount removed per time.
- Bioavailability F = (AUCoral × DoseIV)/(AUCIV × Doseoral) for absolute bioavailability.
- CYP450: inhibition raises substrate levels; induction lowers them. Grapefruit juice inhibits intestinal CYP3A4; rifampicin induces CYP3A4.
- Toxicology: LD50 is a median lethal dose; therapeutic index = TD50/ED50. Antidotes: N-acetylcysteine for paracetamol, naloxone for opioids, atropine for organophosphates.
Worked example
A 500 mg IV bolus gives an initial plasma concentration C0 of 25 mg/L. Vd = 500/25 = 20 L. For a 70 kg patient, Vd = 20/70 ≈ 0.29 L/kg, consistent with distribution into extracellular fluid. If concentration falls from 100 to 25 mg/L in 8 h, that is two half-lives, so t½ = 4 h.
Traps that cost marks
- Confusing potency with efficacy; a more potent drug is not necessarily more effective.
- Saying a competitive antagonist lowers Emax; it does not.
- Using total drug concentration when interpreting Vd for highly protein-bound drugs.
- Mixing up zero-order and first-order half-life; zero-order half-life changes with concentration.