Quinupristin-dalfopristin: an overview.

Synercid (RP 59500), the first injectable streptogramin antibiotic, is composed of two semisynthetic pristinamycin derivatives, quinupristin and dalfopristin. Individually, each component has bacteriostatic activity against staphylococci and streptococci, but together, the agents exhibit synergy, leading to bactericidal activity. The combination drug, however, is bacteriostatic against Enterococcus faecium and has poor activity against Enterococcus faecalis. Despite a short half-life, an extended postantibiotic effect allows the agent to be dosed every 8-12 hours. Both drugs are largely hepatically metabolized and excreted in bile. Although not metabolized by cytochrome P450 3A4, quinupristin-dalfopristin can inhibit agents that are metabolized through this pathway. Dosage adjustments may be necessary in patients with hepatic dysfunction. Alterations in renal function have minimal effects on the agent's pharmacokinetics. Adverse events include arthralgia, myalgias, and infusion-related pain. Based on available data, quinupristin-dalfopristin appears to have a role in treating severely ill patients with infections due to multiresistant gram-positive pathogens.