Altered central nervous system pharmacology of methotrexate in childhood leukemia: another sign of meningeal relapse.

CSF and plasma antifolate concentrations during 257 intravenous (IV) infusions of high-dose methotrexate were measured in 60 children with acute lymphoblastic leukemia. In 49 children who have never had evidence for CNS leukemia, the mean steady-state CSF to plasma methotrexate ratio was 0.013 (SD = 0.01). In contrast, 11 children with overt meningeal leukemia had a 12-fold higher mean ratio of 0.157 (range, 0.013 to 0.844, p less than .01). In the group of patients studied, all of those with a CSF methotrexate concentration greater than 2 SD above the mean either had leukemic cells in the CSF or subsequently developed this condition. In two patients, overt CNS leukemia was preceded by a high CSF:plasma drug ratio at a time when there was no cytologic or clinical evidence for CNS leukemia. As previously observed with intrathecal methotrexate, we conclude that overt meningeal leukemia increases CSF drug concentrations during IV methotrexate therapy. An elevated CSF to plasma ratio may be useful to predict imminent CNS relapse or to verify completeness of response to therapy.