Paper I
2024 December (Supplementary) (2019 Scheme) · 100 marks · 180 min

Question

Enumerate four factors that modify drug action giving suitable examples for each.

Q104 marksShort Answers

Answer

  • Age — neonates have immature renal/hepatic elimination, prolonging half-life (e.g. chloramphenicol → grey baby syndrome); the elderly have declining renal function and altered receptor responsiveness, raising adverse-effect risk.
  • Body size — dose calculated on body weight (or BSA for a few drug classes, chiefly anticancer drugs) since the same absolute dose gives a different effective concentration depending on distribution volume.
  • Genetics (pharmacogenetics) — dose needed for the same effect can vary several-fold on a purely genetic basis, e.g. slow/fast acetylator status for isoniazid, or G6PD deficiency precipitating hemolysis with oxidant drugs.
  • Route of administration — e.g. propranolol given IV bypasses the extensive first-pass hepatic metabolism it undergoes orally, producing a much greater effect at an equivalent dose.

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