THE PREVENTION OF RADIOSURGERY-INDUCED NAUSEA AND VOMITING BY ONDANSETRON - EVIDENCE OF A DIRECT EFFECT ON THE CENTRAL-NERVOUS-SYSTEM CHEMORECEPTOR TRIGGER ZONE

Nausea and emesis are significant side effects in patients undergoing stereotactic radiosurgery for brain lesions in the region of the chemo receptor trigger zone (area postrema of the brain). Even with the curr ent antiemetic treatment (prochlorperazine +/- corticosteroids), those side effects remain significant. The purpose of this study is twofold : [1] to evaluate the efficacy of ondansetron in inhibiting nausea and emesis in stereotactic radiosurgery patients and [2] to demonstrate t hat ondansetron's locus of action is the central nervous system (CNS) chemoreceptor trigger zone in the area postrema. In a pilot study, 10 patients receiving greater than or equal to 350 cGy in a single fracti on of radiosurgery to the region of the area postrema received 32 mg o ndansetron iv 1 hour prior to treatment +/- corticosteroids. In a retr ospective analysis these results were compared to those of patients wi th similar features (and matched for radiation dose to the area postre ma and the dose of corticosteroids) who received prochlorperazine +/- corticosteriods. Nine of 10 patients in the ondansetron group had no n ausea or emesis within 48 hours after treatment; one patient experienc ed one episode of emesis. In the prochlorperazine group, eight patient s had symptoms, three patients needed hospitalization or a physician's care for emesis within 24 hours, and five had nausea with no specific treatment. These preliminary results suggest that ondansetron is a sa fe and efficient drug to prevent nausea and emesis in this patient gro up. The precise mechanism of action of ondansetron in these patients i s unknown, but is likely due to the drug's serotonin-blocking effect w ithin the CNS. A randomized, prospective study has been started at our institution to confirm these preliminary results.