Influence of ondansetron on thermoregulation during exercise in the heat wearing combat clothing

Ondansetron is a selective serotonin antagonist which has been shown to be an effective antiemetic agent for patients undergoing radiation or chemotherapy treatment. The Canadian Forces together with other NATO Countries have an interest in selecting an antiemetic agent that not only is effective in the prevention of emesis induced by chemical agents or radiation exposure, but also has minimal, if any, side effects. The purpose of this study was to examine the influence of a single 8-mg oral dose of the drug on thermoregulation during exercise in a hot (40 degrees C, 30% relative humidity) environment. Ten unacclimatized males performed a drug and placebo trial in single-blind random order. The sessions involved walking on a treadmill at 4.8 km.h-1 with a 2% elevation for a maximum of 3 h. Subjects wore combat clothing during the trials. Total exposure time was similar for the placebo (177 +/- 6 min) and drug (172 +/- 11 min) trials. Also, the rate of sweat production (0.64 +/- 0.1 and 0.66 +/- 0.1 kg.h-1 for placebo and drug, respectively) and body heat gain (303 +/- 112 and 305 +/- 110 kj for the placebo and drug, respectively) were not different between trials. Rectal temperature increased 1.48 +/- 0.40 degrees C for the placebo and 1.47 +/- 0.37 degrees C for the ondansetron trial. Finally, there was no difference in the mean skin temperature response which increased in both conditions to 37.1 +/- 0.5 degrees C. Under the conditions of this experiment, there is no evidence to suggest that the ingestion of ondansetron influences thermoregulation in a hot environment.