Alternative Pharmacokinetic Metrics in Single-Dose Studies to Ensure Bioequivalence of Prolonged-Release Products at Steady State—A Case Study

(1) Background: this article investigates which PK metrics in a single-dose study (concentration at the end of posology interval, C(τ), partial areas under the curve, pAUCs, or half-value duration, HVD) are more sensitive and less variable for predicting the failure of a prolonged-release product at steady-state that was the bioequivalent for C(max), AUC(0-t) and AUC(0-inf), in the single-dose study; (2) Methods: a cross-over study was performed in 36 subjects receiving desvenlafaxine 100 mg prolonged-release tablets. Conventional (C(max), AUC(0-t) and AUC(0-inf)) and additional (C(τ), pAUCs and HVD) PK metrics were considered after single-dose conditions. Predicted PK metrics at steady state (AUC(0-τ), C(max,ss), and C(τ,ss)) were derived using a population PK model approach; (3) Results: the existing differences in the shape of the concentration–time curves precluded to show equivalence for C(τ,ss) in the simulated study at steady state. This failure to show equivalence at steady state was predicted by C(τ), pAUCs and HVD in the single-dose study. C(τ) was the most sensitive metric for detecting the different shape, with a lower intra-subject variability than HVD; (4) Conclusions: conventional PK metrics for single-dose studies (C(max), AUC(0-t) and AUC(0-inf)) are not enough to guarantee bioequivalence at steady state for prolonged-release products.