US-based Avanir Pharmaceuticals has enrolled the first patient in its Phase II trial of its new investigational drug, AVP-786, for the adjunctive treatment of major depressive disorder (MDD).

AVP-786 is a combination of deuterium modified dextromethorphan and ultra-low dose quinidine.

The ten-week, multicentre, Phase II trial is designed to assess the efficacy and safety of AVP-786 in patients who have had an inadequate response to commonly prescribed antidepressants, such as selective serotonin reuptake inhibitors (SSRIs) and serotonin-norepinephrine reuptake inhibitors (SNRIs).

The randomised, double-blind, placebo-controlled proof-of-concept trial is intended to reduce placebo response rates, a phenomenon commonly observed in depression trials.

"AVP-786 is a combination of deuterium modified dextromethorphan and ultra-low dose quinidine."

Massachusetts General Hospital executive vice-chair of department of psychiatry Dr Maurizio Fava said: "There are millions of people with MDD who remain depressed despite receiving standard antidepressant therapy.

"This is an important clinical study given the properties of AVP-786 and the vast unmet need in this area."

Avanir Pharmaceuticals chief medical officer Dr Joao Siffert said: "With a unique, multifaceted mechanism of action encompassing key neurotransmitter systems involved in regulation of mood, AVP-786 has the potential to offer a new approach for the treatment of patients with depression."

Around 200 patients at approximately 30 sites in the US are expected to be enrolled in the trial, which will use a sequential parallel comparison design (SPCD).

SPCD is a design developed ten years ago by Dr Fava and Dr Schoenfeld at Massachusetts General Hospital and is used in central nervous system (CNS) clinical trials.

Primary efficacy measure of the trial is the Montgomery-Asberg depression rating scale (MADRS) total score, a standard clinical measure of depression.

The trial’s secondary outcome measures include evaluation of disease severity, activities of daily living, and quality of life.