Once-daily morphine shows greater improvement than oxycodone BID for chronic back pain

Morphine extended-release once daily significantly reduced pain among patients with chronic, moderate-to-severe low back pain compared with oxycodone controlled-release twice daily, according to results of a study presented at the 25th Annual Scientific Meeting of the American Pain Society (APS) in San Antonio, Texas. The once-daily opioid also demonstrated significant improvement in sleep scores, said Richard L. Rauck, MD, Carolinas Pain Institute, Winston-Salem, NC.

Patients were randomized to receive morphine (n=203) or twice-daily oxycodone (n=189) titrated upwards for the first 3 to 6 weeks, followed by an 8-week evaluation phase and a 16-week extension. The mean daily doses were 63.7 mg morphine and 53.3 mg oxycodone during the evaluation phase and 86 mg morphine and 79.5 mg oxycodone during the extension. Seventy-nine patients in the morphine group and 95 in the oxycodone group entered the extension phase.

The incidence and severity of opioid-related side effects were similar in both treatment groups, and side effects decreased in patients who continued through the extension phase, Dr Rauck said. Side effects included constipation, dizziness, drowsiness, dry mouth, itchiness, nausea, and vomiting.

While both agents were effective in patients with chronic low back pain, once-daily morphine achieved better pain relief with a lower morphine-equivalent dose than twice-daily oxycodone. The morphine-equivalent dose was 63.7 mg in the morphine group and 80 mg in the oxycodone group during the 8-week evaluation, and 86 mg in the morphine group versus 119 mg in the oxycodone group during the 4-month extension phase.

"The once-daily morphine sulfate dose provides a more convenient dosing schedule and improved drug accountability that may improve patient compliance," Dr Rauck said. He stated that morphine has been shown in previous trials to be associated with less opioid plasma level fluctuation, which may contribute to the improved pain relief and sleep scores observed in this study.