Evaluation of bilirubin displacing effect of indomethacin by determination of erythrocyte-bound bilirubin.

The effect of indomethacin on bilirubin binding to human erythrocytes at different bilirubin/albumin molar ratios varying from 0.5-3.0 was studied. Progressive addition of indomethacin produced a linear increase in erythrocyte-bound bilirubin. This increase was more pronounced up to 280 microM drug concentration at all molar ratios being maximum at higher bilirubin/albumin molar ratio. On the other hand, percent increase in erythrocyte-bound bilirubin produced by the drug was found to be maximum at lowest bilirubin/albumin molar ratio and decreased on increasing bilirubin/albumin molar ratio. From these results we conclude that indomethacin induces displacement of bilirubin from albumin, thus increases bilirubin binding to human erythrocytes to a significant degree even at lower concentrations.