Bioavailability of cyclophosphamide and vincristine after intraperitoneal administration in cats

Cyclophosphamide and vincristine are widely used intravenous chemotherapeutic agents in both human and veterinary oncology. Although intravenous administration of these chemotherapeutics is the gold standard in most treatment protocols, this route of administration has several disadvantages (e.g. long infusion times and risk of extravasation). Therefore, alternative routes have been explored in the past. Recently, good clinical results were achieved with intraperitoneal (i.p.) administration of cyclophosphamide and vincristine in cats. However, the bioavailability following i.p. administration of cyclophosphamide and vincristine providing proof of principle has not been investigated and is the focus of the present study. The pharmacokinetics of cyclophosphamide and vincristine after i.p. and intravenous administration was investigated in six cats in a cross-over study by analysis of plasma levels of cyclophosphamide and vincristine after simultaneously administration of 0.6 mg/m vincristine and 200 mg/m cyclophosphamide. The median bioavailability on i.p. administration was 76% for cyclophosphamide and 100% for vincristine. Median areas under the curve for i.p. and intravenous administration were 11.4 and 16.0 ng h/ml for cyclophosphamide and 16.7 and 16.5 ng h/ml for vincristine, respectively. No specific i.p. administration-related adverse events were observed after i.p. administration. The high bioavailability of both cyclophosphamide and vincristine after i.p. administration and the absence of specific i.p. administration-related side effects suggest that i.p. administration is a suitable route of systemic chemotherapy for both chemotherapeutics. These results are promising and may serve as a stepping stone for the investigation of the pharmacology, safety, and efficacy of i.p. administration of cyclophosphamide and vincristine in humans.