Dextromethorphan mitigates phantom pain in cancer amputees.

BACKGROUND

Hyperexcitability of N-methyl-D-aspartate (NMDA) receptors may play a role in the persistence of phantom pain. Dextromethorphan (DM) blocks NMDA receptors.

METHODS

Eight cancer and two noncancer amputees with established, disabling phantom pain received oral DM 60 or 90 mg twice daily (BID) in a three-period double-blind crossover placebo-controlled trial. This followed an open-phase trial in which either dose was given three times daily if pain relief during the double-blind phase was <50% of pretreatment intensity. Patients then underwent a 3-month phase of treatment with the best regimen and a subsequent 1-month posttreatment follow-up.

RESULTS

All patients reported a >50% decrease in pain intensity, better mood, and lower sedation in each treatment phase. Four individuals reported this level of pain relief with the 60-mg and one with the 90-mg BID regimen during the double-blind phase, whereas two amputees benefited from the 60-mg and three from the 90-mg thrice-daily regimen in the open-phase trial. One reported exacerbation of pain with the 90-mg BID regimen, and three reported pain rebound at the 1-month posttreatment follow-up phase. Three patients stopped all previous analgesic use during the study.

CONCLUSIONS

Persistent phantom pain probably involves NMDA receptor hyperexcitability because DM 120 to 270 mg/day mitigated the pain satisfactorily.