Clinical pharmacology of very low dose methotrexate for use in rheumatoid arthritis.

The clinical pharmacokinetics of methotrexate, particularly when the drug is used at low doses for nonmalignant disease, are complicated and require extensive study. Bioavailability of the drug may be influenced--at least in part--by food intake. Biliary excretion can compensate for decreased renal excretion of methotrexate to some degree. However, further studies of the renal excretion of methotrexate are needed.