The bioavailability of oral intermediate-dose methotrexate. Effect of dose subdivision, formulation, and timing in the chemotherapy cycle.

The oral bioavailability of methotrexate is variable and may be dose-dependent. The absorption of 'interval' oral methotrexate, which is given between cycles of chemotherapy, is unknown. The bioavailability of oral methotrexate has been studied in eight patients, acting as their own controls, to assess the effect of subdivision of the dose, the formulation, and the timing of the methotrexate within the chemotherapy cycle. The mean bioavailability for all the oral methods of administration was 28.2% +/- 3.7% compared with the same dose given IV. Absorption was uninfluenced by subdivision of the dose, liquid or tablet formulation, or administration on day 1 or day 10 of the chemotherapy cycle.