Effects of phenytoin on vection-induced motion sickness and gastric myoelectric activity.

The purpose of this study was to test the prophylactic effects of a single low dose of phenytoin on motion sickness. In this double-blind study, fasted male subjects who were susceptible to motion sickness were given either a 200-mg tablet of phenytoin (N = 19) or a placebo (N = 16). Electrogastrograms (EGG's) were recorded predrug, postdrug (4 h after ingestion of drug), before drum rotation, and during drum rotation. During testing, subjects were exposed to an optokinetic drum which was stationary for 8 min and which then rotated at 10 rpm for 16 min. The results showed that the phenytoin subjects had a lower mean subjective symptom score than the placebo group (5.8 vs. 7.1), but the difference was not significant. However, 6 of 16 placebo subjects requested early termination of drum rotation due to symptom severity, whereas only 2 of 19 phenytoin subjects terminated testing prematurely (X2 = 3.89, p < 0.05). The phenytoin group showed no increase in gastric tachyarrhythmia, the pattern of gastric myoelectric activity that usually accompanies nausea, during drum rotation, whereas tachyarrhythmia doubled for the placebo group. In conclusion, we have demonstrated that a single low dose of phenytoin prevents the development of gastric tachyarrhythmia and decreases the intensity of motion sickness symptoms.