A new antifungal medication is being tested in Phase I clinical trials. Examination of the pharmacokinetic propeies of the drug reveals that the half-life of the drug is 6 hours. If a continuous intravenous infusion of this drug were staed on a research subject, how long would it take to reach 75% of steady state?
The rule of thumb is that the plasma concentration will reach 50% in one half-life, 75% in two half-lives, 87.5% in three half-lives, etc., so that the difference between the current drug level and 100% halves with each half-life. In this instance, it takes two half-lives to reach 75%. The half-live of this drug is 6 hours, so two half-lives is 12 hours. Ref: Buxton I.L., Benet L.Z. (2011). Chapter 2. Pharmacokinetics: The Dynamics of Drug Absorption, Distribution, Metabolism, and Elimination. In L.L. Brunton, B.A. Chabner, B.C. Knollmann (Eds), Goodman & Gilman's The Pharmacological Basis of Therapeutics, 12e.
3
6
9
12