Avanir Pharmaceuticals has reported safety and efficacy results of its AVP-923 medication in the study entitled "Efficacy and Safety of Dextromethorphan/Quinidine (AVP-923) at Two Dosage Levels for Diabetic Neuropathic Pain: A Double-Blind, Placebo-Controlled, Multicentre Study."

AVP-923 is a combination of dextromethorphan (DM) hydrobromide (an uncompetitive NMDA receptor antagonist and sigma-1 receptor agonist) and low dose quinidine (Q) sulfate (a CYP2D6 enzyme inhibitor).

In the 13-week Phase III randomised double-blind placebo-controlled trial, 379 adults with daily symmetric diabetic peripheral neuropathy (DPN) leg pain were administered DMQ 45/30mg, or DMQ 30/30mg once daily for seven days and twice daily thereafter.

The trial evaluated efficacy measures, including four pain rating scales applied daily using patient diaries, and another two applied at five clinic visits, and also determined safety and tolerability by adverse event reports, physical examination, electrocardiogram and clinical laboratory tests.

The study demonstrated that DMQ 45/30mg was found superior to placebo, including the primary efficacy analysis and sensitivity analyses, and also showed greater leg-pain relief and leg-pain intensity.

The efficacy of DMQ 30/30 mg was numerically less than for 45/30 mg but for most outcomes remained greater when compared to placebo.

"Throughout a 13-week trial, AVP-923 was effective, with an acceptable safety profile, for treatment of diabetic peripheral neuropathic pain," said Aziz Shabaini, MD, medical director of the Nerve and Muscle Center, Texas.

"The findings indicate that other fixed-dose combinations of AVP-923 should be studied to improve overall tolerability while maintaining significant efficacy."

Currently, AVP-923 is being studied in a Phase II clinical trial, the PRIME study in central neuropathic pain in patients with multiple sclerosis.

Joao Siffert, MD, senior vice president of research and development at Avanir, said: "These results provide additional rationale in support of the ongoing PRIME study, which is evaluating the combination of dextromethorphan and quinidine in central neuropathic pain in patients with multiple sclerosis."