Measurements of red blood cell methotrexate concentrations and lymphocyte subsets during therapy of rheumatoid arthritis.

: Nine patients with rheumatoid arthritis were treated with low dose oral weekly methotrexate for 6 months. Successful therapy was not associated with changes in concentrations of total circulating lymphocytes nor with alterations of T lymphocytes in the helper-inducer, OKT4, or cytotoxic-suppressor, OKT8, subpopulations. Concentrations of methotrexate in circulating erythrocytes stabilized by 1 month of therapy and this measurement did not correlate with clinical efficacy or methotrexate toxicity in the long-term patient assessments.