Tigecycline belongs to a new class of antimicrobial agents, the glycylcyclines, which are structurally derived from tetracyclines. It is effective against both gram positive and gram negative bacteria, aerobes and anaerobes and bacteria that have developed resistance against the classic tetracyclines. Although there is an increased risk for serious adverse events, tigecycline is important for treatment of patients with complicated infections of moderate severity where other antimicrobials cannot be used.