Table 1:
Antibacterial Agents
Linezolid
(Zyvox)
Quinupristin/Dalfopristin (Synercid)
Mechanism of action Binds to the 50S ribosome at a site that inhibits translation. Binds to sequential sites on the 50S subunit of the ribosome
Mechanism of resistance 23S ribosomal RNA mutations Methylation of the 23S ribosome (mediated by the MLSb gene); active efflux (mef gene); enzyme degradation
Spectrum of activity Enterococcus faecium, E faecalis; Staphylococcus aureus, coagulase-negative staphylococci; streptococci, including multidrug-resistant Streptococcus pneumoniae; Corynebacterium sp, Moraxella catarrhalis, Listeria monocytogenes, Pasteurella multocida, Bacteroides fragilis, and some rapidly growing Mycobacteria species Enterococcus faecium; Staphylococcus aureus, coagulase-negative staphylococci; streptococci, including multidrug-resistant Streptococcus pneumoniae; Listeria monocytogenes, Moraxella catarrhalis, Corynebacterium jeikeium, Mycoplasma pneumoniae, Neisseria meningitidis, Fusobacterium sp, peptostreptococci, Clostridium perfringens
Oral absorption 100% None
Half-life 4 h Quinupristin + metabolites, 3 h; Dalfopristin + metabolites, 1 h
Metabolism Oxidation, 2 inactive metabolites Hepatic, 3 active metabolites (2 quinupristin, 1 dalfopristin)
Excretion Renal 30% unchanged in the urine, metabolites also eliminated renally. Biliary
Clinical side effects Nausea, vomiting, diarrhea, headache Arthralgia, myalgia; phlebitis; nausea
Laboratory abnormalities Thrombocytopenia, leukopenia, anemia Elevated bilirubin, abnormal liver function enzymes
Mechanism of drug interactions Nonselective inhibitor of monoamine oxidase Inhibits cytochrome P-450 3A4 enzyme pathway (not a substrate)
Potential drug interactions Adrenergic and serotonergic agents Cyclosporine, nifedipine, midazolam, terfenidine, protease inhibitors, HMG-CoA reductase inhibitors, other P-450 3A4 substrates
Other considerations Incompatible with amphotericin B, chlorpromazine, diazepam, pentamidine, erythromycin, phenytoin, trimethoprim/sulfamethoxazole, ceftriaxone. Incompatible with saline and heparin; IV lines should be flushed with D5W.
Approved indications
  • Infections due to VRE
  • Nosocomial and community-acquired pneumonia
  • Uncomplicated and complicated skin and skin structure infections
  • VRE bacteremia
  • Complicated skin and skin structure infections caused by staphylococci and S pyogenes
Usual dose 600 mg PO or IV q12h (400 mg IV or PO q12h for uncomplicated skin/skin structure infections)
5-7.5 mg/kg IV q8h
HMG-CoA = 3-hydroxy-3-methylglutaryl coenzyme A; PO = oral; IV = intravenous; D5W = 5% dextrose in water; VRE = vancomycin-resistant enterococci
Copyright 2002 The Cleveland Clinic Foundation

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