Clarithromycin and azithromycin: new macrolide antibiotics.

The chemistry, mechanism of action, antimicrobial spectrum, pharmacokinetics, clinical efficacy, adverse effects, drug interactions, and dosage and administration of clarithromycin and azithromycin are described. Clarithromycin and azithromycin are new macrolide antibiotics that are similar in structure to erythromycin. Compared with erythromycin, clarithromycin demonstrates increased activity against Staphylococcus aureus, streptococci, Legionella pneumophila, Moraxella catarrhalis, and Chlamydia trachomatis. Clarithromycin also has in vitro activity against Mycobacterium avium complex (MAC) and Toxoplasma gondii. Azithromycin has increased gram-negative activity compared with erythromycin, including activity against Haemophilus influenzae, while maintaining activity against gram-positive organisms. Azithromycin also has activity against sexually transmitted organisms including Chlamydia trachomatis. The pharmacokinetic profiles of clarithromycin and azithromycin are characterized by good oral bioavailability, excellent tissue penetration and persistence, and long elimination half-lives, which allow for once-daily or twice-daily dosing. Initial data show that clarithromycin and azithromycin are effective for the treatment of upper-respiratory-tract and lower-respiratory-tract infections and infections of the skin and skin structures. Azithromycin has been shown to be effective for the treatment of sexually transmitted diseases caused by Chlamydia trachomatis. Clarithromycin and azithromycin have been used to treat MAC and Toxoplasma infections in patients with the acquired immunodeficiency syndrome. The most frequently reported adverse effects for both agents have been nausea, diarrhea, and abdominal pain. Oral formulations of clarithromycin and azithromycin have recently been approved by the FDA. Clarithromycin and azithromycin are new macrolide antibiotics that have potential advantages over erythromycin; however, the role of these agents will be better defined as results of more ongoing trials become available for evaluation.