Quinupristin/dalfopristin (Q-D) is a synergistic streptogramin combination (30:70 ratio). It has potent in vitro activity against gram-positive pathogens including vancomycin-resistant Enterococcus faecium (VREF), methicillin-resistant Staphylococcus aureus, and drug-resistant Streptococcus pneumoniae, but not Enterococcus faecalis. A minimum inhibitory concentration of 1.0 μg/mL or less, or a zone size greater than 18 mm, indicates susceptibility. Dosing in the United States (7.5 mg/kg) is every 8 hours for serious or life-threatening VREF infections and every 12 hours for complicated methicillin-susceptible Staphylococcus aureus or Streptococcus pyogenes skin or skin structure infections. To minimize side effects, Q-D is given via a central line for a period of at least 60 minutes. Pediatric use is by compassionate or experimental protocol. Q-D is 80 percent excreted in bile and stool. Q-D use with cytochrome P450 3A4 substrate drugs (eg, cyclosporine A) requires drug concentration monitoring. Avoid concomitant corrected QT interval (QTc)-prolonging drugs metabolized by cytochrome P450 3A4. Efficacy in treating VREF is approximately 70 percent, with underlying patient conditions affecting outcome. Adverse effects include pain and inflammation at the infusion site (~40%), hyperbilirubinemia (~25%), arthralgia and myalgia (~7%), nausea and vomiting (~5%), and diarrhea (~3%). Copyright © 2001 by W.B. Saunders Company