Glutaminergic dysfunction has been shown to be related to the pathphysiology of obsessive-compulsive disorder (OCD). Topiramate is an antiepileptic that inhibits glutaminergic action. The aim of this study is to evaluate the efficacy of topiramate augmentation in patients with treatment resistant OCD.

This augmentation trial was designed as a 12-week randomized, placebocontrolled, double-blind study. Forty-nine patients suffering from OCD who had failed to respond to at least 12 weeks of treatment of an adequate and stable dose of a selective serotonin reuptake inhibitor (SSRI) were randomly allocated to receive topiramate or placebo plus their current anti OCD treatment. Yale-Brown Obsessive Compulsive Scale (Y-BOCS) was the primary outcome measure. Treatment response was defined as 25 % or more decrease in scores of Y-BOCS. The mean dosage of topiramate was 180.15 mg/day (range 100–200 mg/day).

Forty-one patients (20 of 24 in topiramate group; 21 of 25 in placebo group) completed the trial. The topiramate group showed significant improvement over the study period (mean Y-BOCS score at week 12 as compared with baseline: P=.000). Those receiving topiramate experienced a mean decrease of 32.0% in Y-BOCS score, compared with 2.4% decrease for those receiving placebo. Twelve patients in the topiramate group versus no patient in the placebo group were rated as responder.

The results of our study demonstrated that topiramate may augment the therapeutic effect of SSRIs in treatment-resistant OCD patients. However, it should be noted that our study is preliminary and larger double-blind studies are needed to confirm these results.