Morphine effects similar to placebo in rheumatoid arthritis

(HealthDay)—For patients with chronic fatigue syndrome (CFS)/fibromyalgia (FM) or rheumatoid arthritis (RA), morphine has anti-hyperalgesic effects comparable to placebo, according to a study published online July 19 in PAIN Practice.

Linda Hermans, P.T., from Ghent University in Belgium, and colleagues conducted a randomized, double-blind, placebo-controlled trial. Ten patients with CFS/FM, 11 with RA, and 20 controls were randomized to experimental (10 mg morphine/0.2 mg/mL naloxone) and placebo groups.

The researchers found that at baseline, compared with controls, patients with CFS/FM and RA had lower deep tissue pain pressure and higher temporal summation. In both patient groups, morphine had a positive effect only on pressure pain thresholds (PPTs); PPTs increased after placebo, but no effects on other pain parameters were objectified. Neither naloxone nor nocebo had significant effects on PPT, deep tissue pain, temporal summation, or conditioned pain modulation (CPM) in the control group.

"The effect of morphine in central sensitization patients appears limited and could have more effect on a peripheral level. Nevertheless, the morphine effect on experimental pain measures was comparable to the effect of placebo," the authors write. "Naloxone did not significantly affect nociceptive modulation in the healthy participants. These results suggest that temporal summation and conditioned pain modulation are not primarily mediated by opioid mechanisms."

One author disclosed financial ties to the pharmaceutical industry.