The comparison of brand-name and generic formulations of venlafaxine: a therapeutic drug monitoring analysis.

OBJECTIVE

Venlafaxine (VEN) is a widely used antidepressant drug, which is available in both brand-name and generic formulations. Bioequivalence studies indicate some pharmacokinetic variability. However, naturalistic therapeutic drug monitoring studies of different generic formulations are lacking.

METHODS

In 2010, inpatients of the Department of Psychiatry, Psychosomatics, and Psychotherapy, University Hospital of Würzburg, were treated with either slow-release brand-name VEN (Trevilor) or slow-release generic VEN (Venlafaxin Hexal) depending on the respective inpatient ward. Routine therapeutic drug monitoring analyses of both groups were compared after matching samples regarding dose of VEN, gender, age, smoking habits, and evaluation of co-medication.

RESULTS

Both groups did not differ in mean values of VEN, O-desmethyl-VEN (ODV), VEN + ODV serum concentrations, and ODV/VEN ratio. No difference in dose-corrected serum concentrations between generic and brand-name VEN was revealed for males, females, smokers, or nonsmokers. In both groups, Spearman Rho correlation between VEN dose and VEN + ODV serum concentration was moderate but significant (P < 0.001; generic: r = 0.554; brand name: r = 0.668). Within the generic subgroup, females had a significantly higher dose-corrected serum concentration of VEN (U test, P < 0.05), whereas within brand name, no gender influence was detected. Spearman Rho correlation of age and dose-corrected ODV (P < 0.05) and VEN + ODV (P < 0.05) was significant only in the generic group. In the brand-name sample, smokers had significantly lower dose-corrected serum concentrations of ODV (U test, P < 0.01) and VEN + ODV (P < 0.01). In the generic group, smoking habit was without any influence.

DISCUSSION: No differences in serum concentrations in dependence of either VEN formulations suggest a safe and efficient treatment of patients using the evaluated generic VEN. However, differences within one formulation regarding gender, age, and smoking status suggest variability of serum concentrations and thus could endanger safety and efficacy of drug use.