Suvorexant for sleep-onset insomnia or sleep-maintenance insomnia, or both

Efficacy
Suvorexant showed significant evidence of improved sleep onset and sleep maintenance in patients with insomnia in clinical trials. The key efficacy clinical trials with insomnia patients included a phase-IIb dose-finding study,¹⁰ 2 similar 3-month phase-III studies,¹¹ and one 12-month phase-III safety study that incorporated efficacy outcomes.¹² All these trials included subjective sleep measures and all except for the long-term safety study also incorporated polysomnographic assess­ment. The specific sleep laboratory outcomes were latency to persistent sleep (LPS), wake after the onset of persistent sleep (WASO), total sleep time (TST), and sleep efficiency (SE). Subjective sleep outcomes were time to sleep onset (sTSO), wake after sleep onset (sWASO), and total sleep time (sTST). Other exploratory endpoints also were assessed. These efficacy and safety studies mostly were performed at dosages considerably higher than those approved by the FDA.

The dose-finding (phase-IIb) trial was conducted with non-geriatric (age 18 to 64) patients with insomnia in a random­ized, double-blind, crossover design of two 4-week periods with subjects given a nightly placebo or suvorexant (10 mg, 20 mg, 40 mg, or 80 mg).¹⁰ Each of the 4 groups included approximately 60 subjects. The 2 co-primary endpoints were SE at Night 1 and the end of Week 4; secondary endpoints were LPS and WASO. Suvorexant was associated with dos­age-related improvements in SE and WASO compared with placebo at both time points. Carryover effects from the period-1 active drug group complicated the analysis of LPS.

The phase-III efficacy and safety trials were performed with 40 mg high dosage (HD) and 20 mg low dosage (LD) groups for adults and with 30 mg HD and 15 mg LD groups for geriatric (age ≥65) patients.¹¹ Two similarly designed 3-month randomized, double-blind, placebo-controlled pivotal efficacy studies assessed objective and sub­jective sleep measures in 4 groups with non-geriatric (HD and LD) and geriatric (HD and LD) insomnia patients.

After baseline assessment, patients took nightly bedtime doses of placebo; suvorexant, 40 mg or 20 mg (non-geriatric individuals); or suvorexant, 30 mg or 15 mg (geriatric indi­viduals). All subjects kept a daily electronic diary and had polysomnographic recordings performed on Night 1, at the end of Month 1, and at the end of Month 3. Both the indi­vidual studies and combined analyses (2,030 subjects) showed that, in non-geriatric and geriatric patients, HD suvorexant resulted in significantly greater improvement in key subjective and objective measures through­out the study (Table 2,⁹ and Table 3,⁹), with the exception of a single LPS outcome in 1 study, compared with placebo. The LD dosages also demonstrated efficacy, but to a reduced extent.

Subjective sleep outcomes were assessed in a 1-year randomized, placebo-controlled trial with nightly placebo, suvorexant, 40 mg, for non-geriatric, or suvorexant, 30 mg, for geriatric insomnia patients.12 The 1-year phase was completed with 484 subjects. Key efficacy outcomes were sTST and sTSO changes from baseline during the first month of treatment. Compared with placebo, suvorexant dosages demonstrated significantly greater efficacy, improvements that were sustained throughout the year.

Clinical trials found suvorexant to be gen­erally safe and well tolerated.¹³ However, specific safety concerns led the FDA to approve the medication at dosages lower than those assessed in the phase-III studies.¹

Somnolence was the most common adverse event in clinical trials. In the phase- IIb dose-finding study, somnolence was reported in <1% in the placebo group, but was associated with suvorexant in 2% of the 10 mg group, 5% with 20 mg, 12% with 40 mg, and 11% with 80 mg.⁹ In the phase-III combined analysis of the 3-month studies, somnolence was reported by 3% in the placebo group and 7% of non-geriatric patients taking 20 mg or geriatric patients taking 15 mg. Somnolence was reported in 8% of women and 3% of men taking the 15 mg or 20 mg dosage in these stud­ies. The 1-year study was performed only with higher suvorexant dosages (30 mg and 40 mg), in comparison with placebo. In this long-term trial, somnolence was reported by 13% of subjects taking suvorexant and 3% taking placebo.

Additional safety issues in trials included excessive daytime sleepiness, impaired driv­ing, suicidal ideation, sleep paralysis, hyp­nagogic/hypnopompic hallucinations, and cataplexy-like symptoms.⁹ Occurrences of these events are rare but have been reported more often among patients taking suvorex­ant than among those taking placebo.

Unique clinical issues
The U.S. Drug Enforcement Agency has categorized suvorexant as a Schedule IV controlled substance. Although there is no evidence of physiological dependence or withdrawal symptoms with suvorexant, studies with recreational substance abusers have shown that the likeability rating is simi­lar to that of zolpidem.¹³

Contraindication
Suvorexant is contraindicated in patients with narcolepsy.⁹ The underlying pathol­ogy of narcolepsy involves a marked reduction in orexin functioning with corre­sponding excessive sleepiness and related symptoms, such as cataplexy, hypnago­gic hallucinations, and sleep paralysis. Although suvorexant has not been evalu­ated in patients with narcolepsy, the drug might, hypothetically, put patients at higher risk of the full spectrum of narco­lepsy symptoms.

There are no other contraindications for suvorexant.

Dosing
Suvorexant should be taken no more than once a night within 30 minutes of bedtime and with at least 7 hours before the planned wake time.⁹ The recommended starting dosage is 10 mg. If this dosage is well toler­ated but insufficiently effective, the dosage can be increased to a maximum of 20 mg. The 5-mg dosage is recommended for indi­viduals taking a moderate CYP3A inhibitor. Generally, patients should take the lowest effective dosage.