Determination of erythromycin base and 2'-acetylerythromycin in human plasma using high-performance liquid chromatography with electrochemical detection.

A high-performance liquid chromatographic method for the determination of plasma concentrations of erythromycin base and 2'-acetylerythromycin, an ester prodrug of erythromycin, is described. tert.-Butyl methyl ether extracts of 1-ml plasma samples (pH 10) were chromatographed on a C18 reversed-phase column. A three-electrode coulometric detector (oxidation potentials +0.65 and +0.85 V) was used for quantitation. Oleandomycin was used as an internal standard. The method has good precision and accuracy, is linear in the range 0.25-7.5 mg/l and has proved to be suitable for pharmacokinetic studies in humans. Correlation with a microbiological assay was satisfactory (r greater than or equal to 0.95), but the chromatographic method gave ca. 30% higher values.