Saturday, February 20, 2010

Opioids Effective for Neuropathic Pain

Researchers have long contested the effectiveness of opioids as a first-line therapy for neuropathic pain. However, it may be time to put aside doubts: opioids do appear to help relieve neuropathic pain in many cases and the focus should now be on which patients can benefit most and for how long.

In a new report — presented briefly at the AAPM (American Academy of Pain Medicine) annual meeting earlier this month — patients with neuropathic cancer pain obtained consistent, long-term pain control with extended-release (ER) oxymorphone (Opana®). Overall, patients reported pain in the mild range throughout most of a one-year open-label study and only 11% discontinued because of lack of efficacy [Slatkin et al. 2010]. The small trial included 27 patients with neuropathic pain who began long-term treatment with ER oxymorphone following participation in a prior shorter-term study. Dose adjustments to improve pain control or tolerability were allowed throughout the 52-week extension phase. The median oxymorphone dose increased from 80 mg/d at baseline to 160 mg/d at 52 weeks — such increases were deemed largely consistent with the nature of the disease — and pain relief remained largely unchanged throughout followup. Eleven patients (41%) reported at least one treatment-related adverse event; most commonly dry mouth, constipation, or fatigue, which were not unexpected. [Disclosure: This clinical trial was supported by Endo Pharmaceuticals, the manufacturer of Opana and a Pain Treatment Topics supporter.]

Other evidence also endorses the potential value of opioids for neuropathic pain. In a recent blogpost we noted a case series of 100 patients treated effectively for 10 or more years with opioid analgesics for chronic noncancer pain; neuropathy was the primary diagnosis in 14 of those patients [see, Followup: Safety of Long-Term Opioid Therapy]. In a much more extensive analysis, the authors of a Cochrane Systematic Review examined 23 good quality trials of oral opioids tested for central or peripheral neuropathic pain [Eisenberg et al. 2006]. While short-term studies provided only equivocal evidence regarding the efficacy of opioids in reducing the intensity of neuropathic pain, intermediate-term studies (up to 70 days) demonstrated significant efficacy of opioids over placebo. Reported adverse events typical of opioid therapy (eg, nausea, drowsiness, constipation) were common but not treatment limiting in most patients (89%).

As with most research in the pain management field, investigations of opioids for neuropathic pain have been over-represented by small trials or case series reports and/or studies covering relatively brief time periods. Certainly, further and better research is needed; meanwhile, there does not appear to be compelling evidence against the consideration of opioid analgesics among first-line therapies that can be effective in select patients for cancer- or noncancer-related neuropathies.

References:
> Eisenberg E, McNicol E, Carr DB. Opioids for neuropathic pain. Cochrane Database Syst Rev. 2006;19(3):CD006146 [
abstract here].
> Slatkin N, et al. "Long-term management of neuropathic cancer pain with oxymorphone extended release: Results of a 1-year open-label extension trial" AAPM 2010; Abstract 117. Also reported in: Bankhead C. AAPM: Opioid Gains Long-Term Control of Neuropathic Cancer Pain. MedPage Today [online]. February 2010 [
available here].