Indomethacin and protein binding of methotrexate.

Indomethacin, a non-steroidal anti-inflammatory drug is known to increase the efficacy and toxicity of methotrexate, the widely used anti-cancer drug in man. The mechanism for this interaction has not been clearly established. However, since these drugs bind with albumin, a possible displacement of methotrexate by indomethacin from albumin might explain this interaction. To investigate the possible interaction an in-vitro protein-binding displacement study was carried out in 17 normal volunteers and in two groups of eight cancer patients. One group of patients had active disease and the other was in complete clinical remission. Serum samples were obtained and protein levels estimated. The protein binding of methotrexate was measured alone and with indomethacin using equilibrium dialysis. Statistical analysis of results suggested that the binding of methotrexate is not influenced by indomethacin, confirming that methotrexate is not displaced by indomethacin.