A clinical pharmacologist is gathering pharmacokinetic data during clinical trials of a new antimicrobial agent. He has already determined that the half-life of this drug is 4 hours. He began a continuous intravenous drip 24 hours ago at a rate of 10 mg/min. Blood tests after 24 hours reveal that the patient's drug plasma concentration is 20 mg/L. What is the clearance of this agent?

You must be familiar with the maintenance dose equation, to answer this question: M.D. = Cl x Cpss/F, where M.D. = maintenance dose Cl = clearance Cpss = plasma concentration at steady state F = bioavailability In this case, M.D. is 10 mg/min; F, or how much drug is absorbed, is 1 (100%) because drugs administered I.V. are completely absorbed. (F becomes impoant when drugs are given orally.) Cpss = 20 mg/L; it takes 4 -5 half-lives to achieve steady state, so this drug has been administered for a time period equaling 6 half-lives. Solving, 10 mg/mL = Cl x 20 mg/mL Cl = 0.5 L/min