Effect of allopurinol on the toxicity of high-dose 5-fluorouracil administered by intermittent bolus injection.

The effect of allopurinol pretreatment on the toxicity of 5-fluorouracil (5-FU) was examined in a clinical trial. Twenty-three patients were given bolus infusions of 5-FU every two weeks in doses that produced mild toxicity (0.8-1.9 g/m2). On alternate courses patients were pretreated with allopurinol either 300 mg two hours prior to and 10 hours after 5-FU, or 300 mg every 8 hours for 4 doses starting 24 hours before 5-FU. Seventeen and 20 pairs of courses were evaluable from the 2- and 24-hour pretreatment groups, respectively. Allopurinol did not produce a significant degree of protection against 5-FU-induced myelosuppression or mucositis on either dose schedule. Neurotoxicity manifesting as both cerebellar and encephalopathic signs and symptoms was the most important toxicity encountered and was dose-limiting for 5-FU on this schedule. Mean oxipurinol serum concentrations at the time of 5-FU administration were 24 microM and 104 microM for the 2- and 24-hour allopurinol pretreatment schedules respectively. Allopurinol increased the T 1/2 of 5-FU by a mean of 67% in three of the four patients studied. Pretreatment with allopurinol did not reduce the toxicity of 5-FU administered as an intravenous bolus.