BIOAVAILABILITY OF ONCE-DAILY VENLAFAXINE EXTENDED-RELEASE COMPARED WITH THE IMMEDIATE-RELEASE FORMULATION IN HEALTHY ADULT VOLUNTEERS

Two open-label, randomized, crossover studies, one single- and one mul tiple-dose, were conducted to assess the relative bioavailability of t wo formulations of once-daily venlafaxine extended release (XR) 75 and 150 mg compared with the immediate-release (IR) formulation of venlaf axine. Healthy adults (12 men, 12 women) aged 18 to 45 years were enro lled in each study. Frequent blood samples were taken for determinatio n of the plasma concentrations of venlafaxine and its active metabolit e, O-desmethylvenlafaxine (ODV). In the single-dose study, the 2 x 75- mg XR formulation and the 150-mg XR formulation were bioequivalent wit h respect to the rate and extent of absorption of venlafaxine and the formation of ODV, and the area under the plasma concentration-time cur ve (AUC) of both XR formulations and the AUC of the IR formulation als o were bioequivalent after normalization for dose. In the multiple-dos e study, the three XR formulations were also bioequivalent with respec t to the rate and extent of absorption of venlafaxine and formation of ODV, and the AUC of all three XR formulations compared with the AUC o f the IR formulation also showed bioequivalence. Overall, the once-dai ly venlafaxine XR formulations provided the same total exposure (measu red by AUC) to both venlafaxine and ODV. Thus it can be predicted that patients will obtain the same response with the XR formulations as wi th the IR formulations.