Incidence of sterile hemorrhagic cystitis in tumor-bearing dogs concurrently treated with oral metronomic cyclophosphamide chemotherapy and furosemide: 55 cases (2009-2015).

OBJECTIVE To determine the incidence of sterile hemorrhagic cystitis (SHC) in tumor-bearing dogs concurrently treated with oral metronomic cyclophosphamide chemotherapy and furosemide. DESIGN Retrospective case series. ANIMALS 55 dogs. PROCEDURES Record databases of 2 specialty practices were searched to identify dogs treated with oral metronomic cyclophosphamide chemotherapy in conjunction with furosemide for a minimum of 28 days between January 2009 and December 2015. Information extracted from the records included signalment, tumor diagnosis, cyclophosphamide and furosemide dosages, and concurrent medications. Confirmed SHC was defined as the presence of gross or microscopic hematuria and clinical signs associated with lower urinary tract disease in the absence of infection or neoplasia of the urinary tract; the definition for suspected SHC was the same, except the absence of infection or neoplasia of the urinary tract was not confirmed. RESULTS Cyclophosphamide dosage varied from 6.5 to 18.6 mg/m2 once daily to 6.3 to 49.2 mg/m2 every other day. Median duration of cyclophosphamide administration was 272 days (range, 28 to 1,393 days). Median cumulative dose of cyclophosphamide administered was 2,898 mg/m2 (range, 224 to 14,725 mg/m2). Median furosemide dose was 1.4 mg/kg (0.64 mg/lb). Confirmed or suspected SHC was identified in 2 of 55 (3.6%) dogs. Cyclophosphamide administration was discontinued for the dog with confirmed SHC but not the dog with suspected SHC. CONCLUSIONS AND CLINICAL RELEVANCE Results indicated that oral administration of furosemide in conjunction with oral metronomic cyclophosphamide chemotherapy was associated with a low incidence of SHC, which suggested that furosemide may protect against cyclophosphamide-induced SHC.