Rapid determination of indomethacin and salicylic acid in serum by means of reversed-phase liquid chromatography.

A method for the quantitative analysis of indomethacin and salicylic acid in blood serum and urine by high-performance liquid chromatography is described. A C18-bonded silica was used as the stationary phase and mixtures of ethanol, n-butanol and aqueous buffer as the mobile phase. Before injection the serum is deproteinized and extracted in one step. The recovery of the extraction was found to be 88% and 77% for indomethacin and salicylic acid, respectively. The relative standard deviations of the analysis for 0.5 micrograms indomethacin and 5 micrograms salicyclic acid per ml serum were 3.6% and 3.2%, respectively. The detection limits for indomethacin and salicylic acid were 2 ng. This corresponds for both substances to 0.1 micrograms/ml serum for an injection volume of 100 microliters. The method enables simultaneous determination of possibly formed metabolites. A number of concurrently administered drugs do not interfere with the analysis. The interactive effects of co-medication of indomethacin and salicylic acid on the serum concentration of indomethacin is demonstrated by measuring the pharmacokinetic curves.