5-Fluorouracil (5-FU) is used in combination chemotherapy protocols for human head and neck cancer and other epithelial neoplasms. However, a paucity of literature describing use of this drug in veterinary oncology exists, likely due to previous reports of fatal neurotoxicity in both dogs and cats, mainly due to ingestion of human creams. The primary aim of this retrospective study was to report the safety of concurrent 5-FU and carboplatin in canine carcinomas. Secondarily, we aimed to look at the efficacy of the combination using overall response rate in treated dogs. Medical records were searched from 2007 to 2017 for dogs treated with both agents; 24 dogs met inclusion criteria. Carboplatin dosages ranged from 180 to 250 mg/m (median 200 mg/m ); 5-FU dosage was 150 mg/m . Fourteen dogs had myelosuppression, ranging from Grade I to asymptomatic Grade IV; thrombocytopenia was more common than neutropenia. Gastrointestinal upset was uncommon, with only seven dogs having Grade I or II nausea, vomiting or diarrhoea. No cases were hospitalized for any of the above toxicities. One dog had an episode of ataxia, which could not be differentiated between otitis and 5-FU neurotoxicity. This protocol is well tolerated. Response rate in the gross disease setting was 43% (three complete responses, three partial responses). Prospective analysis of this combination protocol, and potentially 5-FU with other platinum agents, is warranted in the treatment of canine carcinomas.

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