Early‐Onset 5‐Fluorouracil Toxicity in a Patient Negative for Dihydropyrimidine Dehydrogenase Mutations: The Clinical Course of Reversal with Uridine Triacetate

An antimetabolite pyridine analog, 5‐fluorouracil (5‐ FU ), is used to treat solid tumors. Early toxicities may occur at standard doses of 5‐ FU due to dihydropyrimidine dehydrogenase ( DPD ) deficiency. Uridine triacetate, approved by the Food and Drug Administration in 2015, is an oral prodrug of uridine, a pharmacologic antidote for 5‐ FU toxicity. To our knowledge, this is the first case report that documents the clinical course of a patient treated with uridine triacetate to reverse early‐onset 5‐ FU toxicity negative for DPD mutations. We describe the case of a 73‐year‐old man with anal cancer treated with standard‐of‐care chemotherapy and radiation. Two days after completion of his initial 5‐ FU infusion, the patient developed severe mucositis and extreme fatigue, followed by a rapid decline in his blood cell counts and fevers. The patient was initiated on uridine triacetate 86 hours after completion of his 5‐ FU infusion. Over a 10‐day hospital length of stay, the patient's absolute neutrophil count recovered to within normal limits, and his mucositis significantly improved. At follow‐up visits, the patient denied any residual symptoms of 5‐ FU toxicity. We describe the patient's clinical course from hospital presentation to 31 days after initiation of uridine triacetate.