Motion sickness remains a significant problem for aircrew both in the flying environment (airsickness) and for aircrew deployed at sea (seasickness). While some anti-motion-sickness medications provide reasonable efficacy, adverse neurocognitive effects limit their use in military personnel engaged in safety-sensitive operational roles such as flying. The purpose of this study was to assess the impact on psychomotor performance of promethazine, meclizine, and dimenhydrinate and to determine if the addition of pseudoephedrine or damphetamine to promethazine would ameliorate its adverse effects.
There were 21 subjects (11 men, 10 women), aged 22-59, who were assessed for psychomotor performance on 4 tasks as well as with sleepiness and drug side-effects questionnaires. Psychomotor testing was conducted prior to, and for 7 h after, ingestion of a single dose of each of placebo, promethazine 25 mg, meclizine 50 mg, dimenhydrinate 50 mg, promethazine 25 mg plus pseudoephedrine 60 mg, and promethazine 25 mg plus d-amphetamine 10 mg.
Relative to placebo, promethazine, meclizine, and promethazine plus pseudoephedrine impaired performance on all four tasks [serial reaction time (SRT), logical reasoning (LRT), serial subraction (SST), and multitask (MT)]. Dimenhydrinate impaired performance on the SRT only. Promethazine plus d-amphetamine did not impair performance on any task nor did it result in increased sleepiness. The times to recovery of normal performance for SRT with promethazine, meclizine, dimenhydrinate, and promethazine plus pseudoephedrine were > 7.25, 7.25, 4.25, and 7.25 h, respectively; for LRT were > 7.25, > 7.25, ns, and 7.25 h; for SST were > 7.25, > 7.25, ns, and 7.25 h; for MT were 7.25, 7.25, ns, and 7.25 h. Recovery times to baseline sleepiness levels for promethazine, meclizine, dimenhydrinate, and promethazine plus pseudoephedrine were 7.25, > 7.25, 6.25, and > 7.25 h.
Only promethazine plus d-amphetamine was free from impact on psychomotor performance and did not increase sleepiness.