Cmax/AUC is a clearer measure than Cmax for absorption rates in investigations of bioequivalence.

In bioequivalence studies, the maximum concentration (Cmax) is shown to reflect not only the rate but also the extent of absorption. Cmax is highly correlated with the area under the curve (AUC) contrasting blood concentration with time. Therefore, use of the Cmax/AUC ratio is recommended for assessing the equivalence of absorption rates. The ratio is independent of both intrasubject variations and possible differences in the extent of absorption and reflects only the contrast between the absorption and disposition rate constants (ka/k).