Discuss the pharmacokinetic factors that affect drug half-life.
Half-life (t½) is the time required to change the amount of a drug in the body by one-half during elimination. Candidates were expected to discuss the two main factors which affect drug half-life, namely volume of distribution and clearance. Marks were awarded for the formula (t½ = 0.693 x Vd /CL), the factors which affect the volume of distribution and drug clearance but not for a discussion of factors affecting drug absorption.
The college did not ask the candidates to define half-life in the question, but they defined it in their answer. According to the official text (Birkett et al, 2009), "Half-life is the time take for the amount of the drug in the body (or the plasma concentration) to fall by half".
Half-life is described by the equation:
Half-life of drugs is therefore influenced by the following factors
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