Central effects of the H1-antihistamine, cetirizine

Effects of the H1-antihistamine, cetirizine, were studied on daytime alertness and performance to establish whether the drug would be suitable for use by air personnel and others involved in skilled activity.

The investigation was carried out in six healthy volunteers, and the effects of the drug (5, 10, and 15 mg) were studied on sleep latency, subjective sleepiness, digit symbol substitution, tracking and vigilance from 0.5 h to 7.5 h after ingestion. The study was placebo-controlled and double-blind with a six-way cross-over design. Promethazine (10 mg) was used as an active control to establish the sensitivity of the experimental procedures.

Promethazine (10 mg) decreased the mean level of vigilance over the day, increased objective and subjective sleepiness from 1.5 to 5.5 h, and impaired tracking 5.5 h after ingestion. Cetirizine (10 and 15 mg) led to shortened sleep latencies over the day, and at 7.5 h sleep latencies were shorter with 10 mg cetirizine than with placebo. Subjective sleepiness with cetirizine was increased compared with placebo after 5 mg at 1.5 h, 10 mg at 7.5 h, and 15 mg at 5.5 h and when meaned over the day. Tracking was impaired with 5 and 15 mg cetirizine 0.5 h after ingestion.

The study failed to establish dose-response effects of cetirizine, but it is evident that cetirizine is not free of central activity over the therapeutic range, and so its use by air personnel is not recommended.