An interaction of ondansetron and dexamethasone antagonizing cisplatin-induced acute and delayed emesis in the ferret.

1. Cisplatin, 5 mg kg-1, i.p., administered as a single treatment, induced an acute (day 1) and delayed (days 2 and 3) emetic response in the ferret that was used to investigate the potential anti-emetic activity of ondansetron and dexamethasone and their interaction over a three day period. 2. Ondansetron, 1 mg kg-1, i.p., administered three times per day in two experiments, antagonized significantly the retching and vomiting that occurred on days 1 and 2 by 60-76 and 73-84%. On the third day of treatment there was a trend for a 38% reduction in one experiment and a 74% reduction in the other. 3. There was a trend for dexamethasone, 1 mg kg-1, i.p., administered as a single daily injection for three days, to reduce by 37% the retching and vomiting response that occurred on day 1, the reduction of 77% on day 2 achieved significance and dexamethasone non-significantly increased the retching and vomiting response by 46% on day 3. However, dexamethasone 1 mg kg-1 i.p. administered three times per day for three days significantly reduced the retching + vomiting response by 85, 97 and 86% on days 1, 2 and 3 respectively. 4. The combination of dexamethasone, 1 mg kg-1, i.p., as single daily injections with ondansetron, 1 mg kg-1, i.p., administered three times per day improved the control of the retching and vomiting response, significantly reducing the total numbers of retches and vomits by more than 70% over a three day period. The combination of dexamethasone (1.0 mg kg-1) and ondansetron (1.0 mg kg-1), both administered three times daily, abolished cisplatin-induced emesis over the three day period. 5. The three times per day administration of ondansetron, 1 mg kg-1, i.p., plus dexamethasone, 1 mg kg-1, i.p., administered only on day 1 prevented day 1 emesis but did not modify the retching and vomiting that occurred on days 2 and 3. 6. The present results indicate that ondansetron and dexamethasone significantly reduce cisplatin-induced emesis in the ferret during both the acute and delayed phase; drug/co-treatment can exert an additive action to abolish cisplatin-induced emesis. The ferret model may be useful to detect anti-emetic drug action for treatment of chemotherapy-induced acute and delayed emesis in man.