Dexamethasone can potentiate the anti-emetic action of a 5HT3 receptor antagonist on cyclophosphamide induced vomiting in the ferret.

A new group of selective 5HT3 antagonists are proving to be effective anti-emetics for cytotoxic and radiation induced vomiting in both animal models and man. Current anti-emetic regimens often benefit from combination therapy, in particular the efficacy of metoclopramide (which can be a weak 5HT3 antagonist), can be improved by combination with dexamethasone, another anti-emetic. Hence it was of interest to evaluate whether a 5HT3 receptor antagonist GR38032F could be improved by combination with dexamethasone. Vomiting induced by cyclophosphamide in the ferret was observed after pre-treatment with dexamethasone alone or in combination with GR38032F. Animals were also observed for signs of 'nausea'. Dexamethasone alone proved a weak anti-emetic in this system but did have significant effects on 'nausea'. GR38032F has previously been shown to be capable of totally controlling emesis due to cyclophosphamide in the ferret. Here a dose of GR38032F that is not 100% effective was employed; this was shown to have effects on 'nausea' but most interestingly its anti-emetic action was increased by combination with dexamethasone. This may be important for the minority of patients whose vomiting is not completely controlled by GR38032F alone.