Acceptable sampling times at plateau for drug analysis.

1 Two methods of estimating the average plasma drug concentration at plateau Cav are considered. 2 Given an acceptable error in the estimate of Cav, a range of sampling times, rather than a single time, during the dosing interval, can be calculated. This range depends on the variability of the half-life within the patient population, the dosing interval, the error in assay measurement and the therapeutic index of the drug. 3 When the minimum plasma drug concentration is monitored, an estimate of the individual's half-life is needed, unless the dosing interval is short. Then the population half-life may be used to obtain a reasonable estimate of Cav.