Background/Purpose: Fibromyalgia (FM) is a common, chronic pain disorder, however, at the time of this study there was no approved medicine for FM patients in Japan. This study aimed to assess the efficacy and safety of the α₂δ ligand pregabalin for the symptomatic relief of pain in Japanese patients with FM.

Methods: In a randomized, double-blind, multicenter, placebo-controlled phase III trial conducted at 44 centers in Japan, patients aged ≥18 years who had met the 1990 American College of Rheumatology criteria for FM were randomized to receive either pregabalin, starting at 150 mg/day and increasing to a maintenance dose of 300 or 450 mg/day, or placebo, for 16 weeks (3-week dose-escalation/optimization phase; 12-week fixed-dose treatment phase; 1-week taper phase). The primary endpoint was mean pain score at final assessment. Secondary endpoints included Patient Global Impression of Change (PGIC), Fibromyalgia Impact Questionnaire (FIQ), and measures of sleep (quality of sleep score and Medical Outcomes Study-Sleep Scale). Patients completing the double-blind study were eligible for a 53-week open-label extension study to evaluate the longer-term safety and efficacy of pregabalin (maintenance dose 300-450 mg/day).

Results: In total, 498 patients (89% female) were randomized to receive either pregabalin (n = 250; mean age 47.9 years) or placebo (n = 248; mean age 46.7 years). Pregabalin significantly reduced mean pain score at final assessment (p = 0.0046) and at every week during the study (p < 0.025). Key secondary endpoints were also significantly improved with pregabalin treatment compared with placebo, including PGIC (percentage of patients reporting symptoms "very much improved” or "much improved”; p = 0.0078); pain visual analog scale (p = 0.0013); FIQ total score (p = 0.0144); and quality of sleep score (p < 0.0001). The safety profile of pregabalin was consistent with previous clinical trials. Somnolence, dizziness, nasopharyngitis and increased weight were the most frequently reported adverse events; the majority of adverse events were mild to moderate in severity. A total of 106 patients completing the double-blind trial entered the open-label extension study. Total exposure to pregabalin in the open-label study was 100 person-years, with no new patterns in the type, incidence or severity of adverse events observed. Improvements in measures of pain, sleep and physical functioning were also maintained throughout the 53 weeks of the open-label extension study.

Conclusion: Pregabalin, at doses of up to 450 mg/day, was safe and efficacious for the symptomatic relief of pain when compared with placebo in the double-blind trial. Treatment also improved measures of sleep and physical functioning. Treatment was generally well tolerated and no new safety signals were observed over 53 weeks’ treatment in the open-label extension study. Together, these results indicate that pregabalin is an effective treatment option for Japanese patients with FM.

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ACR Meeting Abstracts - https://acrabstracts.org/abstract/efficacy-and-safety-of-pregabalin-in-japanese-patients-with-fibromyalgia-a-randomized-double-blind-multicenter-placebo-controlled-phase-iii-trial-and-open-label-extension-study/