Venlafaxine is the first of a group of antidepressants that show dual reuptake inhibition of serotonin and noradrenaline (SNRIs). Originally marketed in an immediate release (IR) formulation a microencapsulated, extended release (XR) formulation is now available. Significant differences exist between these two formulations with respect to pharmacokinetic parameters which have an impact on clinical use. The XR has lower maximum plasma concentrations (Cmax) and achieves these at a later time (higher Tmax). The longer apparent elimination half-life of the drug after single XR doses suggests that it is suitable for once daily dosing compared with the twice daily dosing regimen required by the IR formulation. With respect to antidepressant efficacy the XR formulation is equivalent to other marketed antidepressants and to the IR formulation. Consistent with its pharmacokinetic properties the use of the XR formulation is associated with less nausea and dizziness at the initiation of therapy. While in clinical usage XR might be expected to increase compliance with medication and to reduce discontinuation syndromes there are few comparative studies for which this has been evaluated. The XR formulation of venlafaxine is no worse than the IR form with respect to tolerability and offers some benefits to patients in terms of ease of use. On the other hand there does not appear to be any increase in the efficacy of the active agent.
Copyright 2004 John Wiley & Sons, Ltd.