Selective histamine H(1) antagonism: a novel approach to insomnia using low-dose doxepin

Doxepin is a tricyclic antidepressant with a subnanomolar affinity for the histamine H(1) (H(1)) receptor. It has a long history of use for depression at doses higher than those needed for antagonism of H(1) receptors. Recent work has focused on its use at low doses (1, 3 and 6 mg) in patients with chronic primary insomnia. Two phase II studies and four phase III studies have investigated its efficacy on both objective and subjective sleep measures in both adults and elderly patients. It was effective on a variety of sleep onset, maintenance and early awakening outcomes and had minimal effects on sleep architecture. There was no signal for tolerance, psychomotor impairment, residual sedation, rebound insomnia or discontinuation symptoms in trials of up to 3 months duration. Doxepin was well tolerated; sedation/sleepiness and headache were the most common adverse events but these were mainly at placebo level or less. Further work is required to establish doxepin's low-dose effect on hypnotic activity.