Roughly one-third of patients with obsessive-compulsive disorder (OCD) fail to experience significant clinical benefit from first-line interventions such as pharmacotherapy with selective serotonin reuptake inhibitors (SSRI) or cognitive behavioral therapy (CBT). Antipsychotic augmentation is the only pharmacological strategy for treatment-refractory OCD with demonstrated efficacy in multiple double-blind trials (2). Antipsychotic augmentation only benefits around 1 in 3 treatment-refractory OCD. Furthermore, OCD patients typically experience the full treatment benefits of first-line interventions only after a time-lag of two to three months. Failure of symptom relief and delay of symptom relief from first-line treatments are sources of substantial morbidity and decreased quality of life in OCD patients.

Converging lines of evidence from neuroimaging, genetic and pharmacological studies support the importance of glutamate abnormalities in the pathogenesis of OCD. In Magnetic Resonance Spectroscopy studies elevated concentrations of glutamate and related compounds have been demonstrated in the caudate nucleus and orbitofrontal cortex of OCD patients compared to normal controls. In genetic studies, single nucleotide polymorphisms within the glutamate transporter gene SLC1A1 have been associated with the diagnosis of OCD. Open-label, pharmacological treatment studies have suggested that glutamate modulating agents such as riluzole, n-acetylcysteine and memantine may be effective in the treatment of OCD.

Ketamine is a potent antagonist of the N-methyl-D-aspartate (NMDA) receptor, a major type of glutamate receptor in the brain. In a placebo-controlled study completed at Yale a single dose of ketamine (0.5 mg/kg, intravenously) had rapid antidepressant effects in depressed patients. In these subjects ketamine infusion produced mild psychotomimetic symptoms and euphoria that dissipated within 120 minutes, while the antidepressant effects of ketamine infusion emerged over the first 180 minutes and persisted over 72 hours. Fifty percent of depressed patients receiving ketamine were treatment responders at Day 3 compared to 12.5% in the placebo infusion group. These results have been replicated in a recent double-blind study performed at NIMH and a third unpublished study conducted by members of our group at Yale.

Our goal is to conduct an open-label study in treatment-refractory OCD to determine if ketamine may be an effective acute anti-obsessional agent.