Using pharmacokinetics in drug therapy III: Estimating dosage regimens and blood levels using the fraction-lost method.

The "fraction of drug lost during dosage interval" method, which yields rapid estimates for drug dosage regimens and blood levels, is described. Estimation of the fraction lost during a dosage interval allows further calculation of dosage regimens and steady-state blood levels. The estimates derived from this method are valid only when the pharmacokinetics of the drug are linear and elimination from the body occurs according to first-order kinetics. Other limitations of the method are discussed.