An update on tetracyclines.

The tetracyclines are a family of related natural products that were originally discovered by virtue of their antibacterial activities. As one of the earliest antibiotics to be marketed after penicillin and streptomycin, and because of their convenient oral dosing, tetracyclines have achieved wide clinical usage. However, this widespread clinical use, in addition to their use in animal feed, and even as an antibiotic spray for fruit and other crops, has produced widespread resistance that ultimately has limited the clinical utility of the entire family of tetracycline antibiotics. More recently, however, there has been renewed interest in this antibiotic class, with attempts being made to identify compounds capable of evading common bacterial resistance mechanisms and to search for potential uses beyond antibacterial therapy. This review will discuss the identification of 9-glycylamido-tetracyclines (glycylcyclines) and related compounds that have successfully evaded most bacterial resistance mechanisms, resulting in the approval of the first glycylcycline, tigecycline, for clinical use.