Background: To evaluate the influence of pretreatment plasma folate concentrations on methotrexate exposure in children with acute lymphoblastic leukemia/non-Hodgkin lymphoma treated with high-dose methotrexate, we assessed time profiles of plasma homocysteine, folate, and vitamin B(12) concentrations in children treated with high-dose methotrexate with leucovorin rescue.
Methods: We analyzed 98 treatment courses. The study endpoints were to determine how methotrexate exposure is related to homocysteine accumulation and whether it is influenced by pretreatment plasma folate.
Results: Peak concentrations of homocysteine increased from the start of the intravenous infusion through cessation of methotrexate therapy up to time point t(42), when this trend was reversed by administration of folinic acid. The area under the curve (AUC) for plasma homocysteine showed decreasing course-to-course tendencies with a statistically significant decrease only between courses 1 and 2 (P <or=0.05), indicating decreased whole-body homocysteine accumulation in response to administration of consecutive methotrexate courses. Therapeutic courses with low initial folate concentrations (<or=10 nmol/L) gave significantly higher responses in homocysteine accumulation expressed both as (hcys)AUC(0-66 h) and the peak t(42) homocysteine concentrations than did courses with initial folate >10 nmol/L. Correspondingly, in the courses with low initial folate, peak plasma concentrations of methotrexate were significantly higher than in courses with high precourse concentrations of plasma folate.
Conclusion: Endogenous pretreatment plasma folate modulates the magnitude of the methotrexate effect, providing support for a "folate overrescue" concept.