Transcept Pharmaceuticals, a specialty pharmaceutical company, has completed patient enrolment in Phase II trial of TO-2061 added as adjunctive therapy for obsessive compulsive disorder (OCD).

TO-2061 is a low-dose formulation of ondansetron, a serotonin subtype 3 (5-HT3) receptor antagonist, which has been approved for the treatment of nausea and vomiting caused by chemotherapy and radiation therapy, and for the prevention of postsurgical nausea and vomiting.

The trial is designed to evaluate safety and efficacy of TO-2061 added as adjunctive therapy in 168 OCD patients who have not adequately responded to first-line treatment with an approved OCD medication.

In the double-blind trial, patients with a documented history of at least six weeks of inadequate response to an approved OCD medication, continued to receive that first line OCD medication during an additional 6-week run-in phase.

Patients who failed to respond during this run-in phase were eligible to be randomised to the 12 week double-blind active treatment phase, during which they will continue to receive first line medication with the addition of ondansetron 0.5mg twice per day, ondansetron 0.75mg twice per day or placebo twice per day, according to the company.

The difference between active and placebo treatment arms in the change from baseline, as measured by the Yale-Brown Obsessive Compulsive Scale (Y-BOCS) is the primary endpoint of the study.

The company expects top-line results of the placebo-controlled study in the first quarter of 2013.

OCD is characterised by a pattern of unwanted and intrusive thoughts that cause distress and consequent repetitive behaviours aimed at reducing this distress.