Toxicity of metronomic cyclophosphamide chemotherapy in a UK population of cancer-bearing dogs: a retrospective study.

OBJECTIVES

The objective of this study was to assess the incidence of toxicity in a group of cancer-bearing dogs treated with metronomic chemotherapy.

MATERIALS AND METHODS

Retrospective review of dogs treated with metronomic doses of cyclophosphamide: between 5 and 15 mg/m /day or every other day for treatment of neoplasia.

RESULTS

Of the 65 dogs included, there were signs of, mostly mild, toxicity in 32 (49%). The most common toxicities were sterile haemorrhagic cystitis (n=16) and gastrointestinal disorders (n=12). Median time to development of sterile haemorrhagic cystitis was 110 days (range 7 to 686 days). Four dogs developed suspected bacterial infections during treatment.

CLINICAL SIGNIFICANCE

Metronomic cyclophosphamide is generally well-tolerated in dogs but the incidence of sterile haemorrhagic cystitis in this study is higher than previously reported. Regular urinalysis is recommended for all dogs receiving cyclophosphamide chemotherapy, as early detection of haemorrhagic cystitis may prevent development of more serious disease.