Abstract
Josamycin (JM) was given orally to 10 rats at a dose of 200 mg/kg. Serum samples were obtained at 60, 120, 180, and 240 minutes after oral administration and JM concentrations in serum were determined by both high-performance liquid chromatography (HPLC) and a microbiological assay. Comparison of the JM concentrations in serum measured with HPLC and microbiological assay by regression analysis yielded a markedly high constant of inclination (Y=8.0719X-0.2995, r=0.9867, where Y is JM concentration obtained with microbiological assay and X is that obtained with HPLC; r is the regression coefficient). The difference indicated that most of the JM was metabolized and that the presence of antimicrobially active metabolites, deisovaleryl-JM being a main constituent which was also measured as JM, plays an important role in the microbiological assay. Thus, the microbiological assay might not be a suitable method for determination of the unchanged antibiotic if it is metabolized rapidly to produce antimicrobially active metabolites.
