IMPORTANCE: It is unclear whether d-cycloserine (DCS), a partial N-methyl-d-aspartate agonist that enhances fear extinction, can augment the effects of exposure-based cognitive behavioral therapy (CBT) for obsessive-compulsive disorder (OCD). OBJECTIVES: To examine whether DCS augments the effects of CBT for OCD and to explore (post hoc) whether concomitant antidepressant medication moderates the effects of DCS. DESIGN, SETTING, AND PARTICIPANTS: A 12-week, double-blind randomized clinical trial with 3-month follow-up conducted at an academic medical center between September 4, 2012, and September 26, 2013. Participants included 128 adult outpatients with a primary diagnosis of OCD and a Yale-Brown Obsessive Compulsive Scale (Y-BOCS) score of 16 or higher. Concurrent antidepressant medication was permitted if the dose had been stable for at least 2 months prior to enrollment and remained unchanged during the trial. The main analysis was by intention-to-treat population. INTERVENTIONS: All participants received a previously validated Internet-based CBT protocol over 12 weeks and were randomized to receive either 50 mg of DCS or placebo, administered 1 hour before each of 5 exposure and response prevention tasks. MAIN OUTCOMES AND MEASURES: Clinician-administered Y-BOCS score at week 12 and at 3-month follow-up. Remission was defined as a score of 12 or lower on the Y-BOCS. RESULTS: In the primary intention-to-treat analyses, DCS did not augment the effects of CBT compared with placebo (mean [SD] clinician-rated Y-BOCS score, DCS: 13.86 [6.50] at week 12 and 12.35 [7.75] at 3-month follow-up; placebo: 11.77 [5.95] at week 12 and 12.37 [6.68] at 3-month follow-up) but showed a significant interaction with antidepressants (clinician-rated Y-BOCS, B = -1.08; Z = -2.79; P = .005). Post hoc analyses revealed that antidepressants significantly impaired treatment response in the DCS group but not the placebo group, at both posttreatment and follow-up (clinician-rated Y-BOCS: t62 = -3.00; P = .004; and t61 = -3.49; P < .001, respectively). In the DCS group, a significantly greater proportion of antidepressant-free patients achieved remission status at follow-up (60% [95% CI, 45%-74%]) than antidepressant-medicated patients (24% [95% CI, 9%-48%]) (P = .008). Antidepressants had no effect in the placebo group (50% [95% CI, 36%-64%] remission rate in both groups). CONCLUSIONS AND RELEVANCE: The findings suggest that antidepressants may interact with DCS to block its facilitating effect on fear extinction. Use of DCS may be a promising CBT augmentation strategy but only in antidepressant-free patients with OCD. TRIAL REGISTRATION: clinicaltrials.gov Identifier: NCT01649895.
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