Antibiotics are used in dermatology for both infectious and noninfectious skin eruptions. Noninfectious skin eruptions, such as acne vulgaris and acne rosacea, are often treated with systemic antibiotics. The mechanism of action is not clear, although tetracycline inhibits li-pases derived from resident flora in the sebaceous folli-cle (Staphylococcus epidermidis, Propionibacterium ac-nes). These lipases cleave irritating fatty acids from triglycerides in sebum, presumably contributing to cuta-neous inflammation.
Topical antibiotics are helpful in acne vulgaris and acne rosacea and probably in reducing the frequency of in-fections related to intravenous catheters. One drug, mupirocin (Bactroban), is effective in treating impetigo contagiosa. Mupirocin binds to bacterial isoleucyl-transfer RNA synthetase and prevents the incorpora-tion of isoleucine into protein sequences. Mupirocin is most effective against gram-positive bacteria. Toxicity is uncommon.
Another topical antibiotic, metronidazole, is effec-tive in the treatment of acne rosacea. Metronidazole is a synthetic nitroimidazole derivative that reduces in-flammation by an unknown mechanism. Other selected topical antibiotics are listed in Table 41.2.