Zaleplon - a review of a novel sedative hypnotic used in the treatment of insomnia

Abstract

Zaleplon (N-[3-(3-cyanopyrazolo[1,5-a] pyrimidin-7-yl) phenyl] -N-ethyl acetamide) is a non-benzodiazepine recently introduced for clinical use. This agent is indicated for the short-term treatment of insomnia. Preclinical studies have shown that the benzodiazepines triazolam and Ro17-1812 can substitute for zaleplon in animals trained to distinguish zaleplon from saline. The benzodiazepine antagonist flumazenil can antagonise the discriminative stimulus effect of zaleplon. These findings suggest that zaleplon is recognised by animals as a benzodiazepine agent. Zaleplon is active after ip. and oral administration in a variety of motor performance tests, including locomotor activity, rotarod and the loaded grid. Zaleplon has been shown to be active in a number of different anticonvulsant models, including the pentylenetetrazole, isoniazid and electroshock models. The compound is also reported to be active against convulsions induced by bicuculline, picrotoxin and strychnine. Studies in anxiolytic models suggest that zaleplon may have weak anxiolytic activity. From preclinical studies, it appears zaleplon possesses a reduced risk of tolerance compared to triazolam, is less likely to potentiate the effects of ethanol and is unlikely to produce amnestic effects. In man, zaleplon is rapidly absorbed and undergoes extensive presystemic metabolism. The compound has a plasma half-life of approximately one hour and is metabolised primarily via the aldehyde oxidase system to form 5-oxo-zaleplon. This metabolite, along with other minor metabolites formed in vivo, do not appear to contribute to the activity of zaleplon. Metabolites of zaleplon are excreted primarily via the urine. Phase I studies suggest that single daytime doses of zaleplon up to 15 mg are well-tolerated. Short-term impairment of performance occurs when zaleplon is administered during the day at doses greater than or equal to 20 mg. However, given the short half-life of the compound, significant impairment of daytime performance is unlikely if zaleplon is administered at bedtime or shortly after retiring for the evening. Results from Phase II/III studies suggest that zaleplon (5 - 20 mg) produces a dose-dependent reduction in sleep latency in patients suffering from primary insomnia. The clinical efficacy of zaleplon persists for at least four weeks at doses of 10 mg and 20 mg. Studies in patients with a history of drug abuse suggest that the abuse potential of zaleplon (at doses above the therapeutic dose range) is similar to that seen with the benzodiazepine triazolam.