Determination of drug half-life while giving doses between blood samples.

Traditional methods of determining drug elimination half-life require that no doses be given between the blood samples, which delays drug administration. This article details a new method to determine drug half-life from blood samples drawn with intervening drug doses, that is, while blood levels are building rather than falling. This method was derived from one-compartment pharmacokinetic modeling to assist regulation of doses of central nervous system drugs whose blood concentrations have clinical meaning, for example, lithium and some antidepressants. It should improve the accuracy and practicality of pharmacokinetic methods to predict desirable steady-state drug doses at start-up and to monitor the total daily drug exposure during followup.