Combined treatment with morphine and gabapentin is more effective at lower doses than either agent alone at controlling neurological pain, according to a report in this week’s issue of The New England Journal of Medicine.

Drugs that are currently used to treat neurological pain are not entirely effective and have side effects that limit the dosage that can be administered, note Dr. Ian Gilron, from Queen’s University in Kingston, Ontario, and colleagues. Thus, there is a need for new drug combinations to combat this problem.

In a study of 57 patients who had painful diabetic neuropathy or neuralgia related to shingles were randomly assigned to receive sustained-release morphine; gabapentin; morphine plus gabapentin; or lorazepam as a placebo. Forty-one patients completed the five-week trial.

At the start of the study, the subjects had an average daily pain score of 5.72 on a 0 to 10 scale. With morphine plus gabapentin at the maxim-tolerated dose, the score improved to 3.06, but with the other treatments the score never fell below 3.70. Similar findings were obtained when the Short-Form McGill Pain Questionnaire was used for assess pain levels.

When given in combination, the maxim-tolerated doses of morphine and gabapentin were significantly lower than when the drugs were used alone, the investigators point out.

At maxim-tolerated doses, morphine plus gabapentin was more likely than gabapentin alone to be linked to constipation and more likely than morphine alone to be associated with dry mouth.

In a related editorial, Dr. Srinivasa N. Raja and Dr. Jennifer A. Haythornthwaite, from Johns Hopkins University in Baltimore, and colleagues comment that the findings clearly show the advantages of combination treatment with gabapentin and morphine. However, the perceived risks of addiction associated with morphine and the “fear of scrutiny by regulatory agencies may present barriers to the acceptance of this combination as first-line treatment.”

SOURCE: The New England Journal of Medicine, March 31, 2005.