Interactions with the protein binding of 7-hydroxy-methotrexate in human serum in vitro

Biochem Pharmacol. 1988 Feb 15;37(4):607-11. doi: 10.1016/0006-2952(88)90132-3.


7-Hydroxy-methotrexate (7-OH-MTX), the major extracellular methotrexate (MTX) metabolite, is 90-95% bound in human serum, with albumin (HSA) as the major binding protein. Reports of an interaction with concomitantly administered non-steroidal antiinflammatory drugs (NSAIDs) during MTX therapy led us to investigate whether these compounds could reduce the binding of 7-OH-MTX in vitro. Equilibrium dialysis experiments demonstrated that naproxen and indomethacin concentration dependently reduced the binding of 1 microM 7-OH-MTX. After ingestion of 1000 mg naproxen, per cent unbound 7-OH-MTX in sera from volunteers increased 2-3-fold in vitro, positively correlated to naproxen concentrations (P less than 0.00015). In addition, etacrynic acid, bilirubin, sulphamethizole and acetylsalicylic acid displaced 7-OH-MTX from its binding protein(s) in a competitive manner. The data suggest that 7-OH-MTX interacts with several exogenous and endogenous substances associated with HSA in human serum. Displacement of 7-OH-MTX from HSA may contribute to the interaction between NSAIDs and MTX.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Adult
  • Humans
  • Indomethacin / pharmacology
  • Male
  • Methotrexate / analogs & derivatives*
  • Methotrexate / blood
  • Naproxen / pharmacology
  • Protein Binding
  • Serum Albumin / metabolism*


  • Serum Albumin
  • Naproxen
  • 7-hydroxymethotrexate
  • Indomethacin
  • Methotrexate