Equivalence of a high-performance liquid chromatographic assay and a bioassay of azithromycin in human serum samples.

Two sensitive methods for the determination of the azalide antibiotic azithromycin in human serum were compared. High-performance liquid chromatography (HPLC) and a microbiological assay were simultaneously applied to 768 serum samples obtained in a clinical study. There was excellent agreement between the azithromycin concentrations measured by HPLC and by the bioassay. The correlation coefficient for the two methods was r2 = 0.96. The precision and the sensitivity of the methods were found to be very similar.