Tachyphylaxis — FRCA Primary MCQ
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Correct answer: D — Rapid reduction in drug response after repeated doses over a short period
Explanation lettering: D = shown as A · E = shown as B · B = shown as D · A = shown as E
Tachyphylaxis is a rapid reduction in responsiveness after repeated drug administration over a short period, so B is correct. It may result from mechanisms such as depletion of a mediator or acute receptor/signalling desensitisation. A gradual reduction during longer exposure (C) is conventionally termed tolerance, although terminology can overlap. A describes pharmacogenetic variation, D describes sensitisation rather than diminished responsiveness, and E describes drug hypersensitivity. Repeated suxamethonium administration can produce tachyphylaxis, shown by the need for a higher infusion rate to maintain blockade; this should not simply be equated with Phase II block, which is a distinct change in the characteristics of neuromuscular blockade.
Reference: Sridharan K. Drugs associated with tachyphylaxis: results from a retrospective pharmacovigilance study using disproportionality analysis. European Journal of Hospital Pharmacy. 2026;33(2):183–186. https://pubmed.ncbi.nlm.nih.gov/35042786/