Small intestinal transit time affects methotrexate absorption in children with acute lymphoblastic leukemia.

Serum methotrexate concentrations have been measured in 28 children with acute lymphoblastic leukaemia (ALL) following PO administration under standard conditions. Small-intestinal transit time, measured by the time taken for lactulose to pass from mouth to caecum, has been related with methotrexate absorption parameters. Small intestinal transit times ranged from 30 to 240 min. Children with longer transit times had later times of peak methotrexate concentration and tended to have a more erratic methotrexate absorption profile with two peaks. There appears to be an optimal transit time between 90 and 105 min for methotrexate absorption, with both faster and slower small-intestinal transit times producing lower peak concentrations as a fraction of the dose.