Methotrexate pharmacokinetics in patients with rheumatoid arthritis.

Few studies have evaluated the pharmacokinetics of low dose oral methotrexate (MTX) therapy. MTX pharmacokinetics were studied in 10 patients with classic rheumatoid arthritis (RA) after a single 7.5 mg oral dose. MTX was rapidly absorbed. Peak concentrations varied considerably, ranging from 0.31-0.72 microM. Measurable drug concentration was found in all patients at 24 h after the dose. CL/F-MTX = 145 +/- 52 ml/min/1.73 m2 and elimination half-life was 4.5 +/- 0.89 h. Oral MTX given as a single weekly dose has predictable pharmacokinetics. Further studies to examine what relationship exists, if any, with efficacy and toxicity of MTX in RA must be undertaken.