Neuropathic Pain Drug for MS Fails to Establish Efficacy in Clinical Trial

An experimental combination treatment for central neuropathic pain (CNP) in multiple sclerosis (MS) patients failed to show superiority to placebo in a phase 2 study, drug developer Avanir Pharmaceuticals, Inc., announced.

According to the biopharmaceutical company, 209 MS patients who enrolled in the Pain Research in Multiple Sclerosis (PRIME) trial were randomized to receive placebo or 1 of 3 dosage forms of the investigational drug AVP-923 (dextromethorphan hydrobromide/quinidine sulfate) on a daily basis for 12 weeks. The primary efficacy endpoint for the study was improvement in patient-reported Numeric Pain Rating Scale scores from baseline, Avanir said.

Although patients treated with AVP-923 saw statistically significant reductions in pain levels and improvements in pain scores at 12 weeks, their counterparts in the placebo arm reported the same outcomes — a “higher than expected” response to the dummy drug that Avanir believed “negatively impacted the study results.”

In light of those inadequate results, Avanir said in a press release that it “plans to review the detailed data … in conjunction with previously gathered data in diabetic peripheral neuropathic pain to determine next steps for the development of AVP-923 in neuropathic pain.” In addition to the drug’s neuropathic pain trials, the company noted that AVP-923 is currently being tested for safety and efficacy in levodopa-induced dyskinesia and agitation in Parkinson’s disease.

Avanir warned that AVP-923 can “cause serious side effects and should not be used in patients with specific cardiovascular risk factors.” The compound drug has not been approved by the US Food and Drug Administration (FDA).