Paper I
2016 February (2010 Scheme) · 40 marks · 120 min

Question

Bioavailability.

Q53 marksShort Notes

Answer

Bioavailability is the fraction (or percentage) of an administered dose of a drug that reaches the systemic circulation in an unchanged/active form, and the rate at which this occurs.

Determinants

  • Route of administration (IV bioavailability = 100%, defined as the reference standard)
  • First-pass hepatic metabolism (reduces oral bioavailability)
  • Drug formulation/dissolution rate
  • GI absorption factors (pH, motility, presence of food, P-glycoprotein efflux)
  • Drug stability in the GI tract

Clinical significance

  • Determines the dose required by different routes to achieve the same therapeutic effect
  • Two formulations of a drug with the same bioavailability and rate of absorption are termed “bioequivalent”
  • Important in generic drug substitution — bioequivalence testing ensures therapeutic equivalence

Formula: Bioavailability (F) = (AUC oral / AUC IV) × 100 (for the same dose)

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