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.
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.
Ten patients with RA taking 7.5 mg MTX orally once weekly had an average 24 h urine excretion of MTX (while taking 300 mg ferrous sulfate twice daily for one week) of 8.44 micromoles compared to 7.65 micromoles for patients taking placebo. The difference was not statistically significant (p = 0.50).
Our results showed no less absorption of MTX for the placebo group compared to the group that took ferrous sulfate. These results do not support the hypothesis that ferrous sulfate interferes with the absorption of oral MTX.