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 chemoreceptor trigger zone (area postrema of the brain). Even with the current 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 that 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 fraction of radiosurgery to the region of the area postrema received 32 mg ondansetron iv 1 hour prior to treatment +/- corticosteroids. In a retrospective analysis these results were compared to those of patients with similar features (and matched for radiation dose to the area postrema and the dose of corticosteroids) who received prochlorperazine +/- corticosteriods. Nine of 10 patients in the ondansetron group had no nausea or emesis within 48 hours after treatment; one patient experienced one episode of emesis. In the prochlorperazine group, eight patients 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 safe and efficient drug to prevent nausea and emesis in this patient group. The precise mechanism of action of ondansetron in these patients is unknown, but is likely due to the drug's serotonin-blocking effect within the CNS. A randomized, prospective study has been started at our institution to confirm these preliminary results.