Reduced citrovorum factor rescue for high-dose methotrexate therapy in childhood malignancies.

Clinical toxicities and pharmacokinetics of methotrexate (MTX), associated with reduced citrovorum factor (CF) neutralization, were studied on 279 infusions in 25 children with various malignancies. MTX, at 1000-8400 mg/m2, was infused during six to 24 hours with multiple schedules of reduced CF rescue. Plasma MTX levels ranged from 7.0 X 10(-5) to 7.0 X 10(-4) M during MTX infusion. The levels declined rapidly with a two-phase elimination pattern (t1/2 = 1.2-2.5 hours, t1/2 = 18-32 hours). The folate level in the plasma ranged from 5 X 10(-7) M to 1.4 X 10(-6) M when CF was administered every six hours or every three hours, respectively. Limited bone marrow suppression was seen in only seven percent of infusions, with moderate elevation of GOT and GPT in 20% of infusions, and stomatitis in only 2.6% of infusions, despite reduction in the total dose of CF from 225 mg to 105 mg and despite delaying CF initiation from nine hours to thirty-six hours after the start of MTX infusion.