Intravenous Ondansetron plus Intravenous Dexamethasone with Different Ondansetron Dosing Schedules during Multiple Cycles of Cisplatin-based Chemotherapy

Background: This study examined whether different ondansetron dosing schedules plusdexamethasone influenced antiemetic efficacy during multiple cycles of cisplatin-based chemotherapy (CT). Antiemetic activities between previous CTand subsequent cycles were compared.Methods: The cross-over study involved 424 patients. Arm A, three doses of 8 mgondansetron given intravenously (IV) at 4-hourly intervals plus dexamethasone20 mg IV at the start of CT, followed by dexamethasone 5 mg IV every12 hours. Arm B, as arm A but the three doses of 8 mg ondansetron weregiven at 24-hourly intervals. For those with complete protection from emesisin both arms, a single dose of 8 mg ondansetron (arm C) was tried during thefollowing CT. Once complete protection of emesis could not be maintained,arm A regimens were administered in the subsequent cycles of CT.Results: There were 384, 377 and 147 patients in arm A, arm B and arm C, respectively.Complete control of acute and delayed nausea/vomiting obtained inarm A were 91.4%/94.8% and 59.6%/70.1%, and in arm B were90.4%/92.3% and 61.3% 72.7%. There was no significant difference inantiemetic efficacy between both arms. Decreased incidence of and delayedonset of nausea on day 2 were observed in arm B (p = 0.002). The emeticseverity during previous CT correlated significantly with those of the subsequentCT. The complete control of nausea/vomiting was maintained in81.6%/72.1% of arm C patients during the following 3rd-6th cycles of CT.Conclusion: No difference in antiemetic efficacy was shown when a triple 8 mg dose ofondansetron was given at 4-hourly intervals or at 24-hourly intervals.However, the latter improved nausea on day 2. A single 8 mg dose ofondansetron can maintain antiemetic efficacy in the majority of completeresponders in arm A and arm B.