dextromethorphan---quinidine-combination and Diabetic-Neuropathies

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.

Topics: Animals; Clinical Trials as Topic; Dextromethorphan; Diabetic Neuropathies; Drug Combinations; Humans; Mood Disorders; Quinidine

To evaluate dextromethorphan coadministered with quinidine as treatment of diabetic peripheral neuropathic pain.. In a 13-week, phase 3, randomized controlled trial, 379 adults with daily symmetric diabetic peripheral neuropathy (DPN) leg pain for ≥3 months received double-blind placebo, dextromethorphan/quinidine (DMQ) 45/30 mg, or DMQ 30/30 mg, administered once daily for 7 days and twice daily thereafter. Efficacy measures included four pain rating scales applied daily using patient diaries, and another two applied at five clinic visits.. On all six scales, DMQ 45/30 mg was significantly superior to placebo, including the primary efficacy analysis, which utilized mixed-effects modeling to test all scores on an 11-point numerical Pain Rating Scale (P < 0.0001). Sensitivity analyses gave consistent results. Efficacy vs placebo was also seen for diary ratings of present pain intensity, and pain interference with sleep and with activities (all P < 0.0001). Among clinic visit assessments, DMQ 45/30 mg demonstrated greater leg pain relief (P = 0.0002) and greater reduction of leg pain intensity (P = 0.0286) vs placebo. The efficacy of DMQ 30/30 mg was numerically less than for 45/30 mg but for most outcomes remained significantly greater vs placebo. Adverse events were mostly mild or moderate and of expected types. Discontinuation for adverse events in the DMQ groups was at least twice as common as placebo.. Throughout a 13-week trial, DMQ was effective, with an acceptable safety profile, for treatment of DPN pain. Other fixed-dose combinations of DMQ should be studied to improve overall tolerability while maintaining significant efficacy.

Topics: Adult; Aged; Aged, 80 and over; Dextromethorphan; Diabetic Neuropathies; Double-Blind Method; Drug Combinations; Excitatory Amino Acid Antagonists; Female; Humans; Male; Middle Aged; Placebos; Quinidine