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Interaction of valproic acid and the antidepressant drugs doxepin and venlafaxine: analysis of therapeutic drug monitoring data under naturalistic conditions

Unterecker, Stefan; Reif, Andreas; Hempel, Susanne; Proft, Florian; Riederer, Peter; Deckert, Jürgen; Pfuhlmann, Bruno

International Clinical Psychopharmacology: July 2014 - Volume 29 - Issue 4 - p 206–211
doi: 10.1097/YIC.0000000000000025

Valproic acid and the antidepressants doxepin and venlafaxine are frequently used psychotropic drugs. In the literature, an influence of valproic acid on serum levels of antidepressants has been described, although studies have focused on amitriptyline. The authors assessed their therapeutic drug monitoring (TDM) database for patients receiving a combination of doxepin or venlafaxine and valproic acid and compared these samples with matched controls without valproic acid comedication in terms of the serum concentration of antidepressants. The mean dose-corrected serum concentration of doxepin+N-doxepin in 16 patients who received valproic acid comedication was higher (2.171±1.482 ng/ml/mg) than that in the matched controls (0.971±0.857 ng/ml/mg, P<0.003). We also found a significant correlation between valproic acid serum level and dose-corrected doxepin+N-doxepin serum level (Spearman’s ρ r=0.602, P<0.014). The mean dose-corrected serum level of venlafaxine+O-desmethylvenlafaxine in 41 patients who received valproic acid comedication did not differ significantly from that of the matched controls (P<0.089), but there was a significant difference between both groups in the dose-corrected serum level of O-desmethylvenlafaxine (1.403±0.665 vs. 1.102±0.444, P<0.017). As a consequence, if a combination of valproic acid with doxepin or venlafaxine is administered, cautious dosing is advisable and TDM should be performed.

Department of Psychiatry, Psychosomatics and Psychotherapy, University Hospital of Würzburg, Würzburg, Germany

Correspondence to Stefan Unterecker, MD, Department of Psychiatry, Psychosomatics and Psychotherapy, University Hospital of Würzburg, Füchsleinstrasse 15, D-97080 Würzburg, Germany Tel: +49 931 201 77810; fax: +49 931 201 77840; e-mail:

Received November 6, 2013

Accepted November 19, 2013

© 2014 Wolters Kluwer Health | Lippincott Williams & Wilkins