5-FU and allopurinol: toxicity modulation and phase II results in colon cancer.

Concurrent administration of allopurinol allows escalation of 5-FU doses in man when 5-FU is given by continuous infusion for 5 days. Forty-nine patients received 81 courses of treatment with 5-FU and allopurinol in phase I and II trials. The dose-limiting toxicity was mucositis; marrow toxicity was mild. Neurotoxicity, possibly related to 5-FU, occurred in eight patients. No responses were seen in 14 evaluable patients with colon cancer, 11 of whom had had prior 5-FU. One patient with Hodgkin's disease had a partial response; one patient with diffuse histiocytic lymphoma had transient disease regression. Although allopurinol does modify the toxicity of 5-FU, permitting dose escalation, it does not increase the therapeutic index in colon cancer. Infusional 5-FU deserves further study in lymphoma.