AVP-923, a combination of dextromethorphan hydrobromide and quinidine sulfate for the treatment of pseudobulbar affect and neuropathic pain.

AVANIR Pharmaceuticals Inc, under license from Irisys Research & Development, is developing AVP-923 (Zenvia, Neurodex) for the treatment of pseudobulbar affect (PBA; in collaboration with Medison Pharma Ltd) and neuropathic pain associated with diabetic peripheral neuropathy. PBA, the main indication of AVP-923, is a neurological disorder characterized by uncontrollable and unpredictable episodes of laughing and/or crying. AVP-923 consists of a combination of the NMDA antagonist/sigma1 receptor agonist dextromethorphan hydrobromide (DM) and the cytochrome P450 2D6 (CYP2D6) enzyme inhibitor quinidine sulfate (Q). DM has been under investigation for several years as a neuroprotective agent in stroke, neurosurgery and amyotrophic lateral sclerosis (ALS); however, it is rapidly metabolized by CYP2D6, reducing the drug's bioavailability at neuronal targets. The inclusion of Q inhibits the rapid first-pass metabolism of DM to increase systemic concentrations of the drug in the plasma and, in theory, increase the potential efficacy. The initial clinical data for AVP-923 in the treatment of PBA demonstrated the combination was effective, but exhibited significant side effects. Of particular concern to the FDA were increased QTc intervals reported in patients dosed with a 30-/30-mg dose of DM/Q. A subsequent phase III clinical trial assessing a lower dose of AVP-923 (20 or 30 mg DM/10 mg Q) for the treatment of PBA in patients with ALS or multiple sclerosis was implemented by AVANIR and demonstrated a favorable safety profile of AVP-923 while maintaining efficacy. Pending approval of the data from the FDA, AVP-923 would be the first FDA-approved treatment for PBA.