Phenytoin for the prevention of motion sickness.

A 43-year-old woman sought advice about the treatment of her sea-sickness. A sea-kayaking enthusiast, she suffers disturbing motion sickness in big seas. The usual remedies have either been ineffective or made her drowsy. A scuba-diving instructor recommended that she try taking pheny-toin the night before going kayaking, and she wonders whether there is any evidence to support this recommendation. The primary search question was " Is phenytoin effective in the prevention of motion sickness? " The ideal studies to answer this question would be randomised controlled trials comparing phenytoin with placebo or comparing phenytoin with other conventional therapies. Search I searched two online databases, MEDLINE and SUM-Search, combining the terms " motion sickness " and " pheny-toin " and limiting the search to studies published in English. The MeSH term " motion sickness " covers a range of conditions, including sea-sickness and travel-sickness. I also searched the websites for two diving-related organisations: Divers Alert Network and Diving Medicine Online. Summary of findings Five original research articles on the use of phenytoin for motion sickness were identified. Diving Medicine Online had a review article on motion sickness that mentioned phenytoin. The first of the five research articles 1 reported a laboratory based placebo-controlled double-blind crossover study using simulated motion. The seven participants were given phenytoin at anticonvulsant levels. Phenytoin was found to be four times as effective as any other single agent in increasing tolerance to motion stress. The second study 2 involved 15 seamen and/or divers who worked for the US National Aeronautics and Space Administration in both small-boat trials (lasting one hour) and operational sea travel (lasting two to four days). Phenytoin was given in loading doses in the 24 hours before the trials and then maintained at anticonvulsant levels through regular serum testing and titrated doses. The small-boat phase of the study, a double-blind trial of phenytoin versus placebo, showed a significant reduction in nausea levels (P = 0.0172). The operational sea-travel phase of the study again showed a convincing advantage of phenytoin over placebo. The third study, 3 a small double-blind crossover study with nine participants, included sea travel as part of a series of exposures to rotational movement, again using the rapid-loading-dose approach to reach anticonvulsant plasma levels of phenytoin. Results showed that phenytoin effectively reduced motion sickness. The fourth study 4 focused on the effects of phenytoin on cognition and performance. Participants (n = 23) …