Ondansetron for the prevention of seasickness in susceptible sailors: an evaluation at sea.

BACKGROUND: Seasickness is a common problem, causing a significant decrement in performance among naval crew. In about 20-60% of crewmembers, symptoms appear with varying intensity depending on the sea state and the duration of the voyage. Recent studies have suggested antiemetic 5HT3 blockers as a possible treatment for motion sickness, emphasizing their minor clinical and cognitive side effects. The purpose of the present study was to evaluate the 5HT3 blocker ondansetron in the prevention of seasickness. METHODS: There were 16 volunteers with a normal otoneurologic examination and no previous medical history of inner ear disease or vertigo who took part in a double blind, randomized, crossover study. During an initial learning phase, the participants practiced on a battery of computerized performance tests until their results stabilized. Ondansetron 8 mg or placebo was administered 2 h before sailing aboard a 500-ton naval vessel in mild sea conditions. Participants did the performance tests and completed a questionnaire evaluating their seasickness symptoms 4 h into the voyage. RESULTS: No statistically significant reduction of seasickness symptoms was demonstrated between ondansetron treatment and placebo (a Wiker score of 2.69 +/- 1.78 and 2.81 +/- 1.97, respectively). There was no statistically significant difference in side effects or the results of the performance tests. CONCLUSION: In this study, ondansetron was not found to be beneficial in the treatment of seasickness. It could be speculated that the mechanism of nausea in seasickness is different from that of toxin-induced nausea.

Vestibular evoked myogenic potential threshold and seasickness susceptibility.

Numerous attempts have been made to find physiological parameters that might predict susceptibility to seasickness. However, to date, no physiological index has been found that can serve as a diagnostic tool for individual susceptibility to motion sickness at the personnel selection stage. A number of studies have demonstrated that linear acceleration in the vertical plane is the most provocative stimulus of motion sickness. The main physiological sensory modality responsible for monitoring vertical acceleration is the saccule. Over the last decade, vestibular evoked myogenic potentials (VEMP) have come to be recognized as a reliable procedure for the evaluation of saccular function. We used the VEMP test to assess otolith responses in 15 seasickness-susceptible (SS) and 15 non-seasickness-susceptible (NSS) healthy male crew members. The SS group exhibited a significantly higher VEMP threshold and a significantly lower peak-to-peak p13-n23 amplitude interval compared with the NSS group. Further analysis by logistic regression found threshold to be the dominant factor associated with seasickness susceptibility. The study demonstrated differences in the VEMP reflex of the SS and NSS groups. The threshold difference may represent an intrinsic mechanistic difference between the vestibular systems of the two groups. Theoretically, increased susceptibility to seasickness may be due to a discrepancy between the various neural systems as a result of reduced otolith responses.