5-Fluorouracil and methotrexate administered simultaneously as a continuous infusion. A phase I study

Infusion delivery systems have been evaluated for administration of many individual chemotherapeutic agents including 5-fluorouracil (5-FU) and methotrexate (MTX). This study combined the two drugs as an admixture, and in a Phase I trial design established a useful dose schedule for each of the component drugs. 5-FU at a fixed dose rate of 300 mg/M2/day was delivered with methotrexate (MTX) at four different dose rates (0.75, 1.0, 1.5, or 2.0 mg/M2/day, respectively). The drug solution was delivered via a subclavian venous access with a portable infusion pump in an ambulatory setting. Twenty-nine patients received a total of 38 courses of the two-drug infusion: 21 courses were delivered with the two agents admixed constantly throughout treatment (Schedule A) and 17 were administered the treatment with 5-FU delivered continuously and MTX added to the 5-FU for alternate 14-day cycles (Schedule B). For the former schedule, dose-rate-limiting toxicity was related to MTX and included stomatitis developing at days 8 to 14 (median, day 8) with the higher dose rates (1.5-2.0 mg/M2/day) and thrombocytopenia developing at days 11 to 56 (median, day 14) at the lowest dose rates (1.0 mg/M2/day). For Schedule B, dose-rate-limiting toxicity was similarly due to the MTX with thrombocytopenia and/or chemical hepatitis developing in six of seven courses of MTX at 1.0 mg/M2/day and in five of ten courses delivered at 0.75 mg/M2/day. On Schedule B the MTX-associated toxicities were reversed when the MTX administration was interrupted and in the face of continued 5-FU infusion. A reasonable dose rate and schedule for continuous infusion of 5-FU combined with MTX is: 5-FU 300 mg/M2/day X 28 days and MTX 0.75 mg/M2/day for days 1 to 14, with cycles administered consecutively each 28 days.