The effect of ingestion of ferrous sulfate on the absorption of oral methotrexate in patients with rheumatoid arthritis.

Objective: To investigate if ingestion of ferrous sulfate, 300 mg twice daily, will reduce the urinary excretion of unmetabolized methotrexate (MTX) in patients with rheumatoid arthritis (RA) who ingest 2 drugs concurrently, and determine if ferrous sulfate interferes with the absorption of oral MTX.

Methods: In this randomized double-blind placebo controlled crossover study, we compared the urinary excretion of unmetabolized MTX in 10 patients with RA who ingested 7.5 mg MTX as their weekly dose and took either ferrous sulfate 300 mg twice daily or placebo.