Zaleplon

Zaleplon was introduced in Sweden and Denmark as a new treatment for insomnia, particularly in patients who have difficulty in falling asleep. Zaleplon is a non-benzodiazepine compound and is the first in a new generation belonging to the pyrazolopyrimidine class, showing therefore fewer benzodiazepine-like side effects. It can be synthesized in 3 steps from the corresponding acetophenone, the key step being the cyclization of the appropriate enaminone with 3-aminopyrazole-4-carbonitrile. Biochemically, Zaleplon is a full agonist at the benzodiazepine o)1 site of the gaba-A receptor complex, but its behavioural profile remains distinct from both benzodiazepine (e.g. Lorazepam) or non-benzodiazepine (e.g. Zopiclone or Zolpidem) sedativehypnotic drugs. Clinical pharmacokinetic analysis showed rapid absorption and elimination. In man, the main metabolic route was oxidative giving the major metabolites 5-oxo Zaleplon and its N-desethyl analog. Both were shown to have no effect at central benzodiazepine receptors and to be rapidly excreted as glucuronides. In patients with chronic insomnia, Zaleplon at 5 and 10 mg/kg significantly reduced sleep latency and improved the quality of sleep compared with placebo without altering the normal sleep architecture. Given its short halflife, the next-day residual effects such as hangover are minimized. It may have some advantages over benzodiazepines regarding unwanted amnesic effects and psychomotor impairment. There was no evidence for the occurrence of rebound insomnia at 10 mg/kg.