CAPILLARY ELECTROPHORETIC DRUG-MONITORING OF METHOTREXATE AND LEUCOVORIN AND THEIR METABOLITES

High-dose methotrexate is an important element of treatment protocols in childhood acute lymphocytic leukemia or osteosarcoma. A capillary e lectrophoretic method has been developed to measure peak levels and th e metabolite pattern in patients with delayed methotrexate elimination . It serves to determine plasma levels of methotrexate, leucovorin and their metabolites, 7-hydroxymethotrexate, 2,4-diamino-N-10-methylpter oic acid and 5-methyltetrahydrofolic acid. For the determination of hi gh concentrations (>10 mu M) protein precipitation by acetonitrile wil l suffice for sample preparation. All other samples undergo solid-phas e extraction and upgrading on C-18 columns. Aminopterin, a therapeutic antecedent of methotrexate, serves as internal standard. Detection is done on a UV detector with a 300 nm filter. Five hundred mu l of seru m are needed to determine 0.2 mu M of a specified substance (0.5 mu M 5-methylterahydrofolic acid) with good precision and accuracy. For pea k levels, 20 mu l of capillary serum are sufficient. (C) 1998 Elsevier Science B.V. All rights reserved.