Methotrexate concentrations in synovial membrane and trabecular and cortical bone in rheumatoid arthritis patients

Objective. To determine methotrexate (MTX) concentrations in the synovial membrane (SM) and cortical and trabecular bone of rheumatoid arthritis (RA) patients. Methods. Ten RA patients (9 women, 1 man; mean ± SD age 49.2 ± 10.6, mean disease duration 13.2 ± 9.9 years) undergoing surgical procedures for rheumatoid articular lesions participated in this study. Mean ± SD MTX treatment duration was 26.4 ± 21.3 months. The day preceding surgery, 10 mg of MTX was administered intramuscularly. During surgery, a mean ± SD of 19.7 ± 2.6 hours after MTX administration, SM, bone fragments, and blood were collected simultaneously. MTX was assayed by fluorescence polarization immunoassay in plasma and tissues. Results. The mean ± SD plasma concentration was 0.0252 ± 0.01 nmoles/ml at the time of tissue sampling. The mean MTX concentration in SM was 0.285 ± 0.159 nmoles/gm. The mean MTX concentrations in trabecular and cortical bone were 0.292 ± 0.164 and 0.286 ± 0.126 nmoles/gm, respectively. Conclusion. After intramuscular administration, high MTX concentrations are found in SM and cortical and trabecular bone of RA patients.