Objective: To determine the pharmacokinetics of a standard oral dose of 7.5 mg in a cohort of patients beginning methotrexate (MTX) and continuing the drug over 24 months.
Methods: Twenty-one patients underwent pharmacokinetic testing after receiving a dose of 7.5 mg of oral MTX and concomitant nonsteroidal antiinflammatory drug (NSAID) therapy. Studies were performed at the time of MTX initiation, and after 6 and 24 months of therapy.
Results: No significant differences with time were observed in area under the serum concentration versus time curve (AUC), maximal MTX concentration achieved postdosing (Cmax) or time to maximal MTX concentration (Tmax). Renal clearance of MTX at 6 months decreased by a mean (+/- SD) of 23.8 (40.3) cc/min (p = 0.014). Creatinine clearance decreased by 8.6 cc/min (17.2) (p = 0.033) at 6 months.
Conclusion: No differences in AUC, Tmax, or Cmax were observed over a 2 year period in patients with rheumatoid arthritis on a standard 7.5 mg dose of MTX. Renal clearance and creatinine clearance both decreased significantly after 6 months of treatment. This effect may be clinically relevant in certain individuals as MTX is renally excreted.