Paper I
2024 August (Supplementary) (2010 Scheme) · 40 marks · 120 min

Question

Explain the factors modifying drug action. Briefly describe newer drug delivery systems (3+3)

Q16 marksEssays

Answer

Factors modifying drug action Inter-individual and intra-individual variation in drug response is the rule, not the exception — arising from several sources:

  • Body size — dose calculated on body weight (or BSA) since the same absolute dose gives a different effective concentration depending on distribution volume.
  • Age — neonates have immature renal/hepatic elimination (prolonged half-life, e.g. chloramphenicol → grey baby syndrome) and a more permeable blood-brain barrier; the elderly have declining renal function, reduced hepatic blood flow, and altered receptor responsiveness, producing a higher incidence of adverse drug reactions.
  • Sex and pregnancy — smaller average body size in women; pregnancy alters absorption, volume of distribution, protein binding, and elimination simultaneously.
  • 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, G6PD deficiency with oxidant drugs).
  • Concurrent disease and drug interactions — altered pharmacokinetics (renal/hepatic impairment) or pharmacodynamic synergism/antagonism with co-administered drugs.
  • Route of administration and cumulation — different routes alter onset/bioavailability; slowly eliminated drugs accumulate with chronic dosing even without a dosing error.

Newer drug delivery systems

  • Controlled/sustained-release formulations — maintain steady plasma levels, reduce dosing frequency (e.g. sustained-release nifedipine).
  • Transdermal systems — continuous delivery bypassing first-pass metabolism (e.g. nitroglycerin, fentanyl patches).
  • Targeted delivery (liposomes, nanoparticles) — direct the drug to the target tissue, reducing systemic toxicity (e.g. liposomal amphotericin B).
  • Implantable/ocular inserts — sustained local release avoiding repeated dosing.

These improve patient compliance, maintain steady therapeutic levels, and reduce systemic adverse effects compared to conventional dosage forms.

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