QUARTERLY BEAT / JULY 2021 ///
WEBINAR HIGHLIGHTS
DR. JUSTINE LEE , DACVECC, DABT CEO, VETgirl, LLC 5-FU Toxicity in Dogs
In this VETgirl Real-Life Rounds webinar entitled “5-FU,” Dr. Justine Lee, DACVECC, DABT reviews the deadly topical toxin, 5-FU.
5-FLUOROURACIL (5-FU) 5-FU, commonly known by the brand names Efudex®, Carac®, Adrucil®, and Fluoroplex®, is a prescription anti-neoplastic medication that is often used for treatment of actinic keratosis or superficial basal cell carcinoma in humans. It is commonly sold in low concentration products (e.g., 0.5- 5%), and works by inhibiting DNA and RNA synthesis and production, resulting in programmed cell death. 1 While IV administration of 5-FU is occasionally used as a chemotherapeutic agent in dogs (e.g., for mammary gland tumor, etc.), it is not recommended for use in cats. Decades ago, topical 5-FU was used in cats for the treatment of squamous cell carcinoma; however, it resulted in severe toxicosis and death due to its narrow margin of safety. When dogs ingest 5-FU, clinical signs can develop quickly - within 30 minutes up to 6 hours; death has been reported as early as 7 hours. 1 Clinical signs and clinicopathologic abnormalities seen with 5-FU toxicosis in dogs include:
TOXIC DOSE The lowest reported toxic (oral) dose in dogs is 6 mg/kg, while the minimal reported lethal dose is 20 mg/kg. One case report did have a dog survive ingestion of 46 mg/kg of 5-FU. 1 That said, the prognosis with 5-FU toxicosis is typically grave in cats and guarded in dogs (with a reported survival in dogs of approximately 25%). Death typically occurs due to secondary complications from the 5-FU such as sepsis (due to leukopenia), increased intracranial pressure (due to persistent seizures), intracranial hemorrhage (due to severe thrombocytopenia), or DIC (due to severe seizures). Unfortunately, most patients present with severe clinical signs, where it is too late to perform decontamination. Therefore, treatment should be aimed at symptomatic supportive care, anti-convulsant therapy, anti-emetics, antidiarrheals, IV fluids (to help maintain perfusion), thermoregulation, broad-spectrum antibiotics, clinicopathologic monitoring, and symptomatic supportive care. If the patient is able to survive the acute crisis, clinicopathologic monitoring is necessary every 3-4 days thereafter for 2-3 weeks, until bone marrow function returns to normal. 1 References 1. Powell LL. 5-Fluorouracil. The Five-Minute Veterinary Consult Clinical Companion: Small Animal Toxicology. Ames, IO: Wiley-Blackwell. pp. 164- 169. NOTE: When in doubt, all drug dosages should be confirmed and cross- referenced with a reference guide such as Plumb’s Veterinary Drug Handbook.
• hypersalivation • anorexia • vomiting • abdominal pain • diarrhea • bloody diarrhea • ataxia
• tremors • seizures • anemia or hemoconcentration • leukopenia • thrombocytopenia
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