D-cycloserine Does Not Improve but Might Slightly Speed Up the Outcome of In-vivo Exposure Therapy in Patients with Severe Agoraphobia and Panic Disorder in a Randomized Double Blind Clinical Trial

D-cycloserine (DCS)-augmented exposure therapy has proven efficacy in the treatment of acrophobia, social phobia, panic disorder and OCD. Here we studied whether DCS can also improve the effect of cognitive behavioral therapy (CBT) in patients with agoraphobia and panic disorder. To this end, 39 patients with the diagnoses of agoraphobia and panic disorder were treated with 11 sessions of CBT including three individual in-vivo exposure sessions (flooding), augmented with either 50mg of DCS (N=20) or placebo (N=19) in a randomized double blind design. Primary outcome was the total score of the panic and agoraphobia scale. Both groups profited considerably from therapy and DCS did not significantly improve this outcome (p=0.475; η(2)p = 0.01). However, there was a statistical trend (p=0.075; η(2)p = 0.17) in the more severely ill patients that DCS accelerated symptom reduction in the primary outcome at post-therapy. No serious adverse effects occurred during the trial. We conclude that in patients with agoraphobia and panic disorder, DCS seems to lack an additional benefit to efficient cbt, probably due to a floor effect. Nonetheless, the acceleration of symptom reduction in severely ill patients might represent a valuable treatment option deserving further investigation.