Uridine triacetate for prevention of 5FU toxicity due to dihydropyrimidine dehydrogenase (DPD) deficiency.

e19560 Background: Dihydropyrimidine dehydrogenase (DPD) catalyzes degradation of 5-fluorouracil (5FU). Patients with complete or partial DPD deficiency (0.1 and 3% of the population, respectively) can experience severe or lethal toxicities to 5FU, and impaired clearance may underlie many of the 1300 US 5FU toxicity deaths each year. Uridine triacetate prevents or diminishes toxicities when orally administered after 5FU overexposure, and has been used successfully as an investigational antidote in >50 patients following accidental overdoses. METHODS A colorectal cancer patient experienced Grade 3 and 4 GI and hematologic toxicities after a 96 hour infusion of 1000 mg/m2 5FU and was found to be DPD deficient (double mutation). The patient subsequently tolerated 50 and 100 mg 5FU bolus treatments in a modified FOLFOX regimen. However, during the second cycle, this DPD-deficient patient inadvertently received 1000 mg 5FU in 1 minute. Life-threatening toxicity was expected. Treatment with uridine triacetate (10 g q6h for 20 total doses) began within 8 hours. RESULTS In marked contrast to his first exposure to 5FU, the patient experienced no mucositis or additional cytopenia. Preclinical and mechanistic data predicted and support this observation. In a mouse model of DPD deficiency using ethynyluracil (2 mg/kg i.p.), a standard therapeutic 5FU dose of 100 mg/kg i.p. was lethal. Treatment with oral uridine triacetate (2 g/kg t.i.d. x 5 d) starting 2, 24 or 72 hours after 5FU resulted in 100%, 80% or 70% survival, respectively. CONCLUSIONS Timely treatment with uridine triacetate appeared to prevent severe 5FU toxicity in a DPD-deficient patient and reduced mortality in DPD-inhibited mice receiving 5FU. Uridine triacetate has been shown previously to protect patients (and mice) from 5FU toxicities following 5FU overdose. Therefore, DPD-deficient patients who have received 5FU should also benefit from uridine triacetate treatment if the overexposure is identified soon enough after 5FU dosing. Therapeutic monitoring of 5FU during or after infusions would permit rapid detection of 5FU overexposure due to DPD-deficiency or other clearance defects, enabling the use of uridine triacetate as a potential antidote.