Are Gram-negative bacilli covered by Zosyn (piperacillin-tazobactam) and Vancomycin?

From the Guidelines

Zosyn (piperacillin-tazobactam) effectively covers most gram-negative bacilli, while vancomycin does not. Zosyn is a broad-spectrum beta-lactam/beta-lactamase inhibitor combination that targets many gram-negative organisms including Pseudomonas aeruginosa, Escherichia coli, Klebsiella species, and other Enterobacteriaceae, as recommended by the World Society of Emergency Surgery and the Surgical Infection Society and the Infectious Diseases Society of America 1. Vancomycin, on the other hand, is primarily effective against gram-positive organisms and has essentially no activity against gram-negative bacilli due to its inability to penetrate the gram-negative outer membrane. When both medications are used together, this combination provides coverage for both gram-positive organisms (primarily from vancomycin) and gram-negative bacilli (from Zosyn). However, certain highly resistant gram-negative bacilli such as carbapenem-resistant Enterobacteriaceae (CRE) or some strains of Acinetobacter baumannii may not be adequately covered by Zosyn alone and might require alternative or additional antimicrobial agents, as suggested by the Infectious Diseases Society of America 1. The typical Zosyn dosing is 3.375g or 4.5g IV every 6-8 hours (adjusted for renal function), while vancomycin is typically dosed at 15-20 mg/kg IV every 8-12 hours with levels monitored for efficacy and safety. It's worth noting that the choice of empirical therapy should consider epidemiological features and the clinical course of infection, and consultation with an infectious diseases specialist is recommended, especially in cases of culture-negative endocarditis 1. Some key points to consider when using Zosyn and vancomycin include:

• Zosyn provides broad-spectrum coverage of gram-negative bacilli
• Vancomycin provides coverage of gram-positive organisms, including MRSA
• The combination of Zosyn and vancomycin provides coverage for both gram-positive and gram-negative organisms
• Certain highly resistant gram-negative bacilli may require alternative or additional antimicrobial agents
• Consultation with an infectious diseases specialist is recommended for complex cases.

From the Research

Coverage of Gram-Negative Bacilli by Zosyn and Vancomycin

• Zosyn (piperacillin/tazobactam) has a broad spectrum of antibacterial activity that includes Gram-positive and Gram-negative aerobic and anaerobic bacteria 2, 3.
• However, piperacillin/tazobactam retains its in vitro activity against broad-spectrum beta-lactamase-producing and some extended-spectrum beta-lactamase-producing Enterobacteriaceae, but not against isolates of Gram-negative bacilli harboring AmpC beta-lactamases 3.
• Vancomycin, on the other hand, is a broad-spectrum antibiotic against Gram-positive cocci, but it does not have activity against Gram-negative bacilli 4, 5.
• The combination of vancomycin with piperacillin/tazobactam has been shown to be effective against certain Gram-positive and Gram-negative bacteria, including methicillin-resistant Staphylococcus aureus (MRSA) and vancomycin-intermediate Staphylococcus aureus (VISA) 4.

Specific Coverage of Gram-Negative Bacilli

• Piperacillin/tazobactam has been shown to be effective against certain Gram-negative bacilli, including Pseudomonas aeruginosa, Haemophilus influenzae, and Enterobacteriaceae 2, 3, 6.
• However, the effectiveness of piperacillin/tazobactam against certain Gram-negative bacilli, such as those harboring AmpC beta-lactamases, is limited 3.
• The combination of vancomycin with piperacillin/tazobactam does not provide additional coverage against Gram-negative bacilli that are resistant to piperacillin/tazobactam 4, 5.

Clinical Implications

• The choice of antibiotic therapy should be based on the suspected or confirmed pathogen and its antimicrobial susceptibility profile 2, 3, 6, 4, 5.
• The combination of vancomycin with piperacillin/tazobactam may be effective against certain Gram-positive and Gram-negative bacteria, but it should be used judiciously and with consideration of the potential risks and benefits 4, 5.