Background Fibromyalgia (FM) is a common and potentially debilitating syndrome characterized by chronic and widespread musculoskeletal pain, fatigue, sleep disturbance, and physical and psychological impairment. The aetiology of FM remains unknown however, central nervous system (CNS) dysregulation is believed to play a key role in the pathogenesis of the condition. Naltrexone, a competitive antagonist of opioid receptors, is a potential novel treatment for chronic pain. More recently, naltrexone has been shown to attenuate the production of proinflammatory cytokines and neurotoxic superoxides via suppressive effects on CNS microglia cells.
Objectives To evaluate the efficacy of naltrexone in the treatment of FM.
Methods Seventy-four consecutive FM patients diagnosed according to the American College of Rheumatology (ACR) 1990 criteria for FM were randomized into 2 groups, the first group(n = 37) received 4.5mg/d of naltrexone and the second group(n = 37) received placebo for 6 months. Patients were excluded from the study if they were taking any opioid analgesic or were pregnant. All subjects underwent a comprehensive clinical examination. Global pain status was assessed separately by the participant and the study physician, who was unaware of the group assignment, with the use of a visual-analogue scale (VAS) (range, 0 to 100, with higher scores indicating greater pain). The number of tender sites (of 18 sites in total) were also determined according to the standardized protocol. The primary end point was a change in pain. The secondary end point was a change in the Fibromyalgia Impact Questionnaire (FIQ) score (ranging from 0 to 100, with higher scores indicating more severe symptoms) at the end of 24 weeks. All assessments were repeated at 24 weeks to test the durability of the response. Safety and tolerability were also assessed.
Results There was a significant reduction in pain in the naltrexone group compared to the placebo group. Mean (±SD) baseline and 24-week VAS scores for the naltrexone group were 65.6± 13.5 and 45.5±14.1, respectively, versus 66.0±13.5 and 55.3±13.9, respectively, for the control group, p<0.001). Of the 37 patients assigned to the naltrexone group, 16 had clinically important improvements in the FIQ total score and quality of life. Mean (±SD) baseline and 24-week FIQ scores for the naltrexone group were 63.7±13.2 and 38.5±16.1, respectively, versus 63.0±13.0 and 57.9±15.6, respectively, for the control group, p<0.001). The drug was well-tolerated with minimal side effects in the form of headache (15% vs 5%) and vivid dreams (33% vs 14%) occurring more often in the naltrexone group.
Conclusions Naltrexone may be an effective and useful treatment for fibromyalgia. However, long-term larger study population studies are required.
Disclosure of Interest None Declared
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