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

Question

Fixed drug combination of drugs

Q104 marksShort Answers

Answer

A fixed-dose combination (FDC) is a formulation combining two or more drugs in a single dosage form at a fixed ratio.

Rationale/advantages: improved patient compliance (fewer tablets, simpler regimen), synergistic or complementary mechanisms (e.g. sulfamethoxazole + trimethoprim — sequential folate-pathway blockade), reduced cost, and — in some cases — reduced individual adverse effects (magnesium hydroxide + aluminium hydroxide, opposite bowel effects offsetting each other).

Disadvantages: inability to titrate each component’s dose independently, risk of masking one component’s adverse effect or interaction, potential for irrational/unjustified combinations without genuine pharmacological rationale, and difficulty adjusting therapy if one component is contraindicated in a specific patient.

Examples: Amoxicillin + Clavulanic acid, Levodopa + Carbidopa, Sulfamethoxazole + Trimethoprim (Cotrimoxazole).

Principle: an FDC is rational only when the combined drugs have a genuine complementary mechanism/rationale and are needed together in most patients at fixed relative doses — irrational combinations are actively discouraged.

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