Suvorexant in Insomnia Co-morbid With Fibromyalgia

It has now become clear that the relation of sleep and pain is bidirectional; acute and chronic pain is associated with disturbed sleep and disturbed sleep enhances pain. Experimental studies have shown that reduced and fragmented sleep in pain-free normals increases their pain sensitivity and daily self-report studies in chronic pain patients have shown a poor night of sleep is followed by enhanced next-day pain. In mediation analyses of large clinical data sets it is found that the sleep-pain side of the bidirectional relation, as opposed to the pain-sleep side, accounts for the greater variance. These data then would suggest that improving sleep in chronic pain disorders should attenuate daytime pain. Most of the drugs used to treat chronic pain facilitate inhibitory central nervous system mechanisms as their primary mechanism of action. Suvorexant, recently approved by the FDA for the treatment of insomnia characterized by difficulties with sleep onset and sleep maintenance, has a unique mechanism of action. Suvorexant is a selective antagonist for orexin receptors (OX1R and OX2R). Orexins are considered to be involved in arousal and maintenance of the waking state. As such, suvorexant may provide unique clinical benefit as a treatment in chronic pain conditions with co-morbid insomnia, and specifically for fibromyalgia with its putative central hyperarousal and hypersensitization. Thus, this project proposes to study objective and clinical measures of sleep, pain, and daytime sleepiness and fatigue in patients with fibromyalgia and co-morbid insomnia while treated short-term with suvorexant 20 mg versus placebo. Those qualifying will receive suvorexant 20 mg and placebo for each of 9 nights in a cross over design with 7 nights of washout between treatments. Overnight sleep recordings (PSGs) will be collected on nights 7 and 8 of each crossover treatment arm to determine objective sleep measures. During the day following night 7 in each arm, a Multiple Sleep Latency Test (MSLT) at 1000, 1200, 1400, and 1600 hr will be conducted and nociceptive sensitivity \[finger withdrawal latency (FWL)\] testing to a radiant heat stimulus (1100 and 1500 hr) will be conducted on day 1 and day 8. Self-reported mood and pain indices will also be completed prior to each FWL test. Primary outcomes to be measured include PSG sleep efficacy and FWL response on both conditions (suvorexant 20 mg versus placebo).