Efficacy and tolerability of adjunctive gabapentin and memantine in obsessive compulsive disorder: Double-blind, randomized, placebo-controlled trial.

BACKGROUND: In the search for additional pharmacologic treatments of patients with obsessive-compulsive disorders (OCD), the glutamatergic system is attracting growing interest. While adjuvant memantine to a standard medication with a selective serotonin-reuptake inhibitor (SSRI) appears to reduce OCD symptoms, the adjuvant effect of gabapentin is less certain. The aim of the present randomized, double-blind and three-arm clinical trial was therefore to assess whether, compared to placebo, gabapentin (GAB) or memantine (MEM) adjuvant to a standard medication with an SSRI (fluoxetine; FLU) might lead to further improvements.

METHODS: A total of 99 outpatients (mean age: 29.59 years; 49.5% females) diagnosed with OCD were randomly assigned to one of the following three conditions: FLU + gabapentin (FLU + GAB); FLU + memantine (FLU + MEM); FLU + placebo (FLU + PLA). Experts rated patients' symptoms of OCD with the Yale-Brown Obsessive-Compulsive Scale (Y-BOCS) at baseline, and 4 and 8 weeks later.

RESULTS: YBOCS scores did not decrease over time. No group differences were observed. However, the significant Time by Group interaction showed that Y-BOCS scores decreased significantly over time in the FLU + PLA group. Response rates did not differ between the three study conditions. Typical side-effects were rash (FLU + MEM), drowsiness (FLU + GAB), anxiety (FLU + GAB; FLU + PLA), and drowsiness plus anxiety (FLU + GAB).

CONCLUSIONS: The present pattern of results suggests that glutamatergic medications such as gabapentin and memantine adjuvant to a standard treatment with an SSRI have no additional positive impact on patients with OCD, as measured with the Y-BOCS. Additionally, side-effects were reported. Future studies should use more fine-grained tools to assess, for example, patients' sleep and cognitive functioning, and patients' view of symptoms.