Adverse events in small dogs treated with a single dose of vinblastine.

Abstract

BACKGROUND: Vinblastine (VBL) is a chemotherapeutic agent commonly used to treat malignant tumors in dogs. Although a maximum tolerated dose of 3.5&#xa0;mg/m2 has been reported, the safety and tolerability of this dose in small dogs remain inadequately characterized. HYPOTHESIS/OBJECTIVES: Retrospectively evaluate adverse events (AEs) associated with a single IV administration of VBL at a dosage of 2.0&#xa0;mg/m2 in dogs weighing <&#x2009;10&#xa0;kg. We hypothesized that AE occurrences in small dogs would be comparable to those reported in phase I studies involving larger breeds. ANIMALS: Forty client-owned dogs weighing <&#x2009;10&#xa0;kg with malignant tumors. METHODS: Adverse events after a single IV VBL administration at a dosage of 2.0&#xa0;mg/m2 were retrospectively evaluated in small dogs with malignant tumors. Myelosuppressive and gastrointestinal AEs were graded using VCOG-CTCAE v2.0 criteria. RESULTS: Neutropenia and thrombocytopenia were observed in 82.5% (33/40) and 5.0% (2/40) of dogs, respectively. Grade 3 or 4 neutropenia occurred in 32.5% (13/40), comprising 15.0% (6/40) with Grade 3 and 17.5% (7/40) with Grade 4 events. Inappetence, vomiting, and diarrhea were reported in 7.5% (3/40), 7.5% (3/40), and 25.0% (10/40) of dogs, respectively, and were generally mild. Febrile neutropenia was noted in 5.0% (2/40) of dogs. CONCLUSIONS AND CLINICAL IMPORTANCE: Vinblastine administered at a dosage of 2.0&#xa0;mg/m2 in small dogs with malignant tumors resulted in gastrointestinal toxicity within clinically acceptable limits, but close monitoring for neutropenia is warranted. These findings suggest that dose escalation of VBL, as reported in larger dogs, may not be feasible in smaller dogs.