Venlafaxine: the relationship between dose, plasma concentration and clinical response in depressive patients.

The relationship between plasma drug level of venlafaxine and daily intake was studied in 89 major depressive inpatients. In addition, changes over time in severity were assessed weekly in a subgroup of 22 depressed patients using the Montgomery and Asberg Depression Rating Scale (MADRS) and the Clinical Global Impression improvement scale. The results indicate a moderate correlation between daily doses and plasma concentrations, together with a higher relationship between improvement on the MADRS scale and concentration. Moreover, plasma concentrations (for venlafaxine and its predominant metabolite, O-desmethylvenlafaxine) up to 400 microg/l can be considered as effective, as already suggested in a previous study. No case of venlafaxine discontinuation occurred during the longitudinal study, and the incidence of adverse event, as estimated by the Target Emergent Symptoms and Side-effects scale, was low, suggesting that the drug is well tolerated for such plasma concentrations.