Liquid-chromatographic determination of indomethacin in blood from newborns with patent ductus arteriosus.

This rapid, accurate "high-performance" liquid-chromatographic procedure is intended for measuring indomethacin in serum from neonates who are receiving indomethacin for symptomatic patent ductus arteriosus. Indomethacin and an internal standard (flufenamic acid) are extracted from serum or plasma with chloroform or diethyl ether at pH 5.0. For the chromatography we used a Waters' Radial Compression Separation System (Radial-NOVA PAK C18 reversed-phase column) and a mobile phase of methanol/sodium acetate buffer (10 mmol/L, pH 3.6), 70/30 by vol. The column effluent is monitored at 254 nm. Both indomethacin and flufenamic acid are eluted within 7 min. Indomethacin can be detected in concentrations as low as 50 micrograms/L, in 100-microL samples. Response varies linearly with indomethacin concentration to at least 2 mg/L. Analytical recovery is 75%; relative recovery is 100%. Precision is excellent. Using this method, we were able to improve the success rate for pharmacological management of symptomatic patent ductus arteriosus, especially in neonates with fast clearance rates for the drug.