Sleep and Pain in Subjects with Fibromyalgia and Comorbid Insomnia: Double-blind, Crossover, Study of Suvorexant 20 mg versus Placebo.

OBJECTIVES The chronic pain disorder, fibromyalgia, is associated with sleep disturbance, typically sleep maintenance. No studies have evaluated the effect of sleep medication on pain sensitivity in this population. Suvorexant, an orexin antagonist, approved for treatment of insomnia was evaluated for effects on both the sleep and pain of fibromyalgia. METHODS Women, 21- 65 yrs old, with fibromyalgia and co-morbid insomnia (n=10) were treated, double-blind, for 9 nights each with suvorexant, 20 mg, and placebo in counterbalanced order. All were in good psychiatric and stable physical health and met American College of Rheumatology 2010 criteria for fibromyalgia and DSM-V criteria for insomnia. A screening 8-hr PSG was used to rule out other sleep disorders. On nights 8 and 9 of each treatment 8-hr PSGs were collected and on days 1 and 8 pain sensitivity was assessed at 1100 and 1500 hr by measuring finger withdrawal latency (FWL) to a radiant heat stimulus at 5 randomly presented intensity levels. RESULTS Suvorexant vs placebo increased total sleep time (7.2 vs 6.7 hrs, p< .05) and reduced wake after sleep onset (37 vs 67 min, p<.04) with no night effects or interaction. Latency to persistent sleep and sleep stage measures were not altered. FWL on both am and pm tests varied as a function of intensity (p<.001). Average FWL (over 5 intensities and both days) was increased relative to placebo on both the am test (13.9 vs 13.1 sec) and pm tests (15.8 vs 14.1 sec, p<.03) following suvorexant the previous night. CONCLUSIONS Suvorexant 20 mg in patients with fibromyalgia, improved sleep time and reduced next-day pain sensitivity on assessments of FWL to a radiant heat stimulus.