Allodynia and hyperalgesia of the central nervous system are thought to result from the activation of N-methyl-D-aspartate (NMDA) receptors. The oral antitussive, dextromethorphan, is a readily available NMDA receptor antagonist known to inhibit wind-up and central hyperexcitability of dorsal horn neurons.
The objective of this study was to determine the efficacy, safety and toxicity of dextromethorphan in the management of chronic pain.
A Canadian adult teaching hospital.
A retrospective chart review and follow-up study conducted from June 1999 to June 2000.
Main Outcome Measures
Primary endpoints included pain control assessed on a 0 to 5 point pain scale and adverse events associated with dextromethorphan.
Twenty-four patients prescribed dextromethorphan as an outpatient for the management of chronic pain were identified and evaluated. Fibromyalgia was the primary indication for dextromethorphan in these patients. The average daily maintenance dose of dextromethorphan prescribed was 150-200mg/day. Six patients were followed over a 12 month period. Data on compliance, efficacy and adverse effects experienced with dextromethorphan were tabulated. Using a 0 to 5 point pain scale, pain was assessed at three month intervals by the patient for a two week period and by a telephone interview conducted by the investigator. Three patients discontinued dextromethorphan after three, four and five months respectively with no improvement in pain control. For those whose pain responded to dextromethorphan, pain scoring decreased an average of one level on a 0 to 5 point pain scale. Patients commonly reported that dextromethorphan did not eliminate pain, but made it more tolerable. Patients noted increased mobility, improved sleep and overall management of pain. Side effects were frequent, but acceptable to the patient.
Dextromethorphan should be reserved as an adjunct for chronic pain associated with fibromyalgia where all other therapies have failed.