Extent and spectrum of the antimicrobial activity of clarithromycin

Clarithromycin, a new semisynthetic macrolide, is lipophilic and achieves concentrations in tissue that are generally 10 times greater than concentrations achieved in serum. Its binding to serum proteins is low and reversible. Clarithromycin has in vitro and in vivo activity against a variety of Gram-positive and Gram-negative bacteria, Mycoplasma, Chlamydia and mycobacteria. 14-Hydroxyclarithromycin, the major metabolite of clarithromycin in humans, is generally as active as clarithromycin against these organisms but is more active in vitro and in vivo than clarithromycin against Haemophilus influenzae. Organisms resistant to erythromycin by plasmid or transposon-encoded methylase, macrolide-lincosamide-streptogramin resistance, are also resistant to clarithromycin. Unlike older macrolides, however, clarithromycin has in vitro and in vivo activity against atypical mycobacteria. The antimicrobial activities of clarithromycin and 14-hydroxyclarithromycin are reviewed in this article.