Interaction of indomethacin with adult human albumin and neonatal serum.

The binding of indomethacin to albumin was investigated at 37 degrees C, pH 7.4. The first stoichiometric binding constant is 2.5 X 10(5) M-1. Indomethacin utilizes both the bilirubin and diazepam binding functions equally. The effect on bilirubin binding to albumin is negligible at therapeutic indomethacin blood levels. Oleic acid does not affect indomethacin binding until the oleate/albumin molar ratio exceeds 2. A method for measuring the reserve albumin equivalent for binding indomethacin is described. Measurement of this reserve binding equivalent in 33 neonatal serum samples shows no significant correlation of the reserve binding to the albumin level. This methodology may be useful in studying the variable response of infants with patent ductus arteriosus to indomethacin.