Doxepin (Silenor): A histamine H1-receptor antagonist for the treatment of insomnia

Nearly 70 million American adults are affected by insomnia, with sleep maintenance difficulty (waking frequently during the night and/or waking too early and being unable to return to sleep) being the most commonly reported night-time symptom. Doxepin 3-mg and 6-mg tablets were approved by FDA in March 2010 to treat both short- and long-term insomnia characterized by difficulties with sleep maintenance in both adults and the elderly. Doxepin works by blocking the histamine H₁-receptor, a mechanism of action different than that of any other currently FDA-approved prescription medication for the treatment of insomnia.

Efficacy. The efficacy of doxepin for improving sleep maintenance is supported by 6 randomized, double-blind studies up to 3 months in duration that included 1,423 subjects, between 18 and 93 years of age, with chronic (n=858) or transient (n=565) insomnia. In these studies, the 3-mg and 6-mg doses of doxepin were consistently found to be superior to placebo as measured by the amount of time spent awake after sleep onset. After discontinuation of doxepin, no signs of rebound insomnia were detected.

Safety. The most common treatment-emergent adverse reactions, reported in ≥2% of patients treated with doxepin, and more commonly than in patients treated with placebo, were somnolence/sedation (6%–9%), nausea (2%), and upper respiratory tract infection (2%–4%). No withdrawal effects or other adverse events indicative of physical dependence were observed in clinical studies. Consequently, FDA has not designated doxepin as a controlled substance. The failure of insomnia to remit after 7 to 10 days of treatment may indicate the presence of a primary psychiatric and/or medical illness, which should be evaluated. As with other sedative/hypnotic agents, those taking doxepin may experience abnormal thinking and behavioral changes, an increased suicide risk and worsening of depression, and impaired alertness and motor coordination.