Studies on the in vitro postantibiotic effect of azithromycin (AZM) and its clinical efficacy

The in vitro postantibiotic effect (PAE) of azithromycin, a newly developed macrolide antibiotic, was examined. The results were as follows: The in vitro PAE of AZM against Staphylococcus aureus Smith, Streptococcus pneumoniae TW 228, and Haemophilus influenzae TW 644 were 0.6, 1.0, and 3.9 hours, respectively, at a dose of 2 MIC, and 1.1, 1.3, and 4.2 hours, respectively, at a dose of 4 MIC. As compared with the control drugs, erythromycin (EM), roxithromycin (RXM), and clarithromycin (CAM), AZM had a shorter PAE against S. aureus Smith and S. pneumoniae TW 228 but a longer PAE against H. influenzae TW 644. In the clinical study, AZM was administered to one patient with pneumonia, but another antibacterial agent was combined during the observation period. Thus the clinical effect was difficult to evaluate. Abnormal laboratory changes probably due to the drug were elevated GPT, ALP, and LDH.