Erythromycin is a macrolide antibiotic that inhibits bacterial protein synthesis by targeting the 50S ribosomal subunit, blocking the progression of nascent polypeptide chains. It is active against a host of bacterial genera, including Streptococcus, Staphylococcus, and Haemophilus (MIC90s = 0.015-2.0 mg/l). Erythromycin (10-40 mg/kg) dose-dependently inhibits the growth of S. aureus in a mouse model of thigh infection. It also inhibits the cytochrome P450 (CYP450) isoform CYP3A4 in vitro with IC50 values of 33 and 27.3 µM for alpha-hydroxytriazolam and 4-hydroxytriazolam formation, respectively, following administration of triazolam, which is known to be metabolized primarily by CYP3A4. Formulations containing erythromycin have been used in the treatment of bacterial respiratory and skin infections, pertussis, and a variety of other bacterial infections.