The new macrolide antibiotics. Azithromycin and clarithromycin.

Azithromycin (Zithromax) and clarithromycin (Biaxin Filmtabs) are new macrolide antibiotics with several advantages over erythromycin. Azithromycin has an expanded spectrum against gram-negative bacilli. Clarithromycin is more active than erythromycin against gram-positive cocci; combination with its 14-hydroxy metabolite enhances its antimicrobial activity. These new agents penetrate well into tissues and concentrate in macrophages and polymorphonuclear leukocytes. They offer improved bioavailability and an extended half-life. The high tissue-to-serum level and extended elimination half-life of azithromycin allow for once-daily dosing and short-course therapy. Clarithromycin and 14-hydroxyclarithromycin maintain high serum levels and tissue-to-serum concentrations. Both of these new agents have been effective in streptococcal pharyngitis, acute sinusitis, acute lower respiratory tract infections, skin and soft-tissue infections, and sexually transmitted diseases. A single dose of azithromycin is effective for genital chlamydial infections. Adverse reactions to these agents have usually been mild and have not included serious organ toxicity. In clinical trials, the rate of premature discontinuation of therapy has been less than observed with erythromycin. Azithromycin and clarithromycin should be used according to the current guidelines of the Food and Drug Administration; their future role will be determined by ongoing laboratory and clinical evaluations.