Half-Life Calculation — FRCA Primary MCQ
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Correct answer: D — 3.5 h
The correct answer is D, 3.5 h. First convert clearance to compatible units: 116.7 mL/min is approximately 7.0 L/h. In a one-compartment model with first-order elimination, the elimination rate constant is kel = CL/Vd, and t1/2 = 0.693/kel = 0.693 × Vd/CL. Thus, t1/2 = 0.693 × 35/7.0 = 3.46 h, which rounds to 3.5 h. Option A, 5.0 h, is the time constant Vd/CL and results from omitting the factor 0.693. Option E approximates using 0.5 rather than ln(2). The other values are inconsistent with the stated clearance and volume of distribution.
Reference: Yalcin N et al. Population pharmacokinetics in critically ill neonates and infants undergoing extracorporeal membrane oxygenation: a literature review. BMJ Paediatrics Open. 2022;6:e001512. https://rcoa.ac.uk/media/51911