• N J Meropol, D Niedzwiecki, D Hollis, R L Schilsky, R J Mayer, and Cancer and Leukemia Group B.
• Divisions of Medical Science and Population Science, Fox Chase Cancer Center, Philadelphia, Pennslyvania, USA. nj_meropol@fccc.edu
• Cancer. 2001 Apr 1; 91 (7): 1256-63.

BackgroundThe oral administration of 5-fluorouracil (5-FU) is hindered by erratic bioavailability due to catabolism of 5-FU by the enzyme dihydropyrimidine dehydrogenase (DPD) in the gastrointestinal tract. Eniluracil is a potent inactivator of DPD which results in 100% oral bioavailability of 5-FU. Leucovorin (LV) is another biochemical modulator of 5-FU that potentiates inhibition of thymidylate synthase, the primary target of 5-FU. The goal of this study was to determine the antitumor activity and toxicity of an oral regimen containing eniluracil, 5-FU, and LV in patients with colorectal carcinoma.MethodsSixty eligible patients who had previously untreated, measurable, metastatic colorectal carcinoma were treated with oral eniluracil 50 mg on Days 1-7, 5-FU 20 mg/m(2) on Days 2-6, and LV 50 mg on Days 2-6. Cycles were repeated at 28-day intervals.ResultsThe overall response rate was 13% (95% confidence interval [CI] = 6, 25%), with 1 complete response and 7 partial responses. Three additional patients had partial responses that were not confirmed at subsequent evaluations. The median time to progression of disease was 4.4 months (95% CI = 3.45, 7.69) and the median survival time was 12.6 months (95% CI = 9.1, 14.75). Grade 3-5 toxicity (1 toxic death) occurred in 51 patients (85%). Grade 4 neutropenia occurred in 25 patients (42%), and 18 patients (30%) had Grade 3-4 diarrhea. Twenty-one patients (35%) were hospitalized for toxicity, and 12 (20%) had febrile neutropenia. Baseline creatinine clearance was associated inversely with severe toxicity (P = 0.001).ConclusionsAlthough antitumor activity was observed, the frequent occurrence of severe toxicity with this regimen limited its clinical utility. Alternate schedules with a more favorable therapeutic index are undergoing clinical testing and should be pursued. The high level of toxicity observed with orally administered low dose 5-FU underscored the potency of eniluracil as a biochemical modulator.Copyright 2001 American Cancer Society.

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