D-Cycloserine for Treatment Nonresponders With Obsessive-Compulsive Disorder: A Case Report

Using pre-treatment de novo threat conditioning outcomes to predict treatment response to DCS augmentation of exposure-based CBT

BACKGROUND

Over a decade and a half of research has resulted in inconsistent evidence for the efficacy of d-cycloserine (DCS), a partial glutamatergic N-methyl-D-aspartate agonist, for augmenting exposure-based cognitive behavioral therapy (CBT) for anxiety- and fear-based disorders. These variable findings have motivated the search for moderators of DCS augmentation efficacy.

METHODS

In this secondary analysis of a previous randomized clinical trial, we evaluated the value of de novo threat conditioning outcomes-degree of threat acquisition, extinction, and extinction retention-for predicting treatment response to exposure-based CBT for social anxiety disorder, applied with and without DCS augmentation in a sample of 59 outpatients.

RESULTS

We found that average differential skin conductance response (SCR) during extinction and extinction retention significantly moderated the prediction of clinical response to DCS: participants with poorer extinction and extinction retention showed relatively improved treatment response with DCS. No such effects were found for expectancy ratings, consistent with accounts of DCS selectively aiding lower-order but not higher-order extinction learning.

CONCLUSIONS

These findings provide support for extinction and extinction retention outcomes from threat conditioning as potential pre-treatment biomarkers for DCS augmentation benefits. Independent of DCS augmentation, the current study did not support threat conditioning outcomes as useful for predicting response to exposure-based CBT.

Enhancement of Psychosocial Treatment With D-Cycloserine: Models, Moderators, and Future Directions

Advances in the understanding of the neurobiology of fear extinction have resulted in the development of d-cycloserine (DCS), a partial glutamatergic N-methyl-D-aspartate agonist, as an augmentation strategy for exposure treatment. We review a decade of research that has focused on the efficacy of DCS for augmenting the mechanisms (e.g., fear extinction) and outcome of exposure treatment across the anxiety disorders. Following a series of small-scale studies offering strong support for this clinical application, more recent larger-scale studies have yielded mixed results, with some showing weak or no effects. We discuss possible explanations for the mixed findings, pointing to both patient and session (i.e., learning experiences) characteristics as possible moderators of efficacy, and offer directions for future research in this area. We also review recent studies that have aimed to extend the work on DCS augmentation of exposure therapy for the anxiety disorders to DCS enhancement of learning-based interventions for addiction, anorexia nervosa, schizophrenia, and depression. Here, we attend to both DCS effects on facilitating therapeutic outcomes and additional therapeutic mechanisms beyond fear extinction (e.g., appetitive extinction, hippocampal-dependent learning).

RANDOMIZED TRIAL OF D-CYCLOSERINE ENHANCEMENT OF COGNITIVE-BEHAVIORAL THERAPY FOR PANIC DISORDER

BACKGROUND

Initial studies have provided a mixed perspective of the efficacy of d-cycloserine (DCS) for augmenting the efficacy of exposure-based cognitive behavioral therapy (CBT) for panic disorder. In this multicenter trial, we examine the magnitude of DCS augmentation effects for an ultra-brief program of CBT.

METHODS

We conducted a double-blind, controlled trial at three treatment sites, randomizing 180 adults with a primary diagnosis of panic disorder to five sessions of treatment, with study pill (50 mg DCS or matching placebo) administered 1 hr prior to the final three sessions. Two booster sessions were subsequently provided, and outcome was assessed at posttreatment and 1-month, 2-month, and 6-month follow-up assessments. The primary outcome was the degree of reduction in the Panic Disorder Severity Scale. Additional analyses examined the role of severity and current antidepressant or benzodiazepine use as moderators of DCS augmentation effects.

RESULTS

DCS augmentation resulted in significant benefit only early in the trial, with no beneficial effects of DCS augmentation evident at follow-up evaluations. We did not find that baseline severity or antidepressant or benzodiazepine use moderated DCS efficacy, but benzodiazepine use was associated with lower efficacy of CBT regardless of augmentation condition.

CONCLUSIONS

Consistent with other recent multicenter trials, the benefit of DCS was less than indicated by pilot study and reflected an acceleration of treatment response evident at treatment endpoint, but no advantage in response over follow-up evaluation. Our results did not support severity or concomitant medication moderators observed in previous trials of DCS augmentation.