Clarithromycin is a broad-spectrum macrolide antibacterial agent which is effective both in vitro and in vivo against the major pathogens responsible for respiratory tract infections. Clarithromycin's principal metabolite is 14-(R) hydroxyclarithromycin (14-OH-clarithromycin). The other metabolite, namely 14-(S) hydroxyclarithromycin is inactive. The purpose of this study was to show the hydroxylation of CLA at the 14 position to form the R and S epimers and to determine the metabolic ratio of 14ROHCLA/CLA and 14SOHCLA/CLA for understanding the metabolization. This study suggest that in healthy adults, the individual variations in therapeutic responses to clarithromycin can be assumed by taking the drug and its metabolites ratios. Clarithromycin and metabolites ratios increase during metabolization.