Does Zosyn (piperacillin/tazobactam) cover Gram-positive organisms?

From the Guidelines

Zosyn (piperacillin-tazobactam) does cover many gram-positive bacteria, though its coverage is not as comprehensive as some other antibiotics specifically targeted at gram-positive organisms. Zosyn effectively treats infections caused by susceptible strains of Streptococcus species (including S. pneumoniae) and methicillin-susceptible Staphylococcus aureus (MSSA) 1. However, it does not cover methicillin-resistant Staphylococcus aureus (MRSA), Enterococcus faecium, or other resistant gram-positive organisms. Some key points to consider when using Zosyn for gram-positive coverage include:

• Zosyn's primary strength is its broad-spectrum activity, combining the extended-spectrum penicillin piperacillin with the beta-lactamase inhibitor tazobactam, making it particularly effective against many gram-negative bacteria, anaerobes, and some gram-positives 1.
• This combination allows it to overcome resistance mechanisms in many bacteria that produce beta-lactamase enzymes.
• For infections where resistant gram-positive coverage is specifically needed, Zosyn would typically need to be combined with other antibiotics like vancomycin, linezolid, or daptomycin 1.
• The use of vancomycin or other gram-positive active agents should be guided by clinical judgment and susceptibility patterns, as their overuse can contribute to the development of resistance 1.

From the FDA Drug Label

Antimicrobial Activity Piperacillin and tazobactam has been shown to be active against most isolates of the following microorganisms, both in vitro and in clinical infections [see Indications and Usage (1)] Aerobic bacteria Gram-positive bacteria Staphylococcus aureus (methicillin susceptible isolates only) The following in vitro data are available, but their clinical significance is unknown At least 90 percent of the following bacteria exhibit an in vitro minimum inhibitory concentration (MIC) less than or equal to the susceptible breakpoint for piperacillin and tazobactam against isolates of similar genus or organism group However, the efficacy of piperacillin and tazobactam for injection in treating clinical infections caused by these bacteria has not been established in adequate and well-controlled clinical trials Aerobic bacteria Gram-positive bacteria Enterococcus faecalis (ampicillin or penicillin-susceptible isolates only) Staphylococcus epidermidis (methicillin susceptible isolates only) Streptococcus agalactiae† Streptococcus pneumoniae† (penicillin-susceptible isolates only) Streptococcus pyogenes† Viridans group streptococci†

Zosyn (piperacillin/tazobactam) has activity against certain Gram-positive bacteria, including:

• Staphylococcus aureus (methicillin susceptible isolates only)
• Enterococcus faecalis (ampicillin or penicillin-susceptible isolates only)
• Staphylococcus epidermidis (methicillin susceptible isolates only)
• Streptococcus agalactiae
• Streptococcus pneumoniae (penicillin-susceptible isolates only)
• Streptococcus pyogenes
• Viridans group streptococci 2

From the Research

Zosyn Coverage of Gram-Positive Bacteria

• Zosyn, a combination of piperacillin and tazobactam, has a broad spectrum of antibacterial activity that includes Gram-positive and Gram-negative aerobic and anaerobic bacteria 3, 4.
• The combination is effective against many Gram-positive bacteria, including Staphylococcus spp., Bacillus spp., and Streptococcus spp. 5.
• However, its activity against certain resistant Gram-positive bacteria, such as methicillin-resistant Staphylococcus aureus (MRSA), may be limited 6, 7.
• Studies have shown that the combination of piperacillin/tazobactam with vancomycin may be synergistic against MRSA, but the effectiveness of this combination may depend on the specific strain of MRSA 7.

Specific Gram-Positive Bacteria Covered by Zosyn

• Oxacillin-susceptible Staphylococcus spp.: Zosyn has activity against these bacteria, with an MIC50 of 0.12-0.5 μg/ml 5.
• Bacillus spp.: Zosyn has activity against these bacteria, with an MIC50 of 0.5 μg/ml 5.
• Vancomycin-susceptible enterococci: Zosyn has activity against these bacteria, but with a higher MIC50 (>4 μg/ml) 5.
• Streptococcus spp.: Zosyn inhibits all Streptococcus spp. strains at ≤16 μg/ml, including penicillin-resistant strains 5.

Limitations of Zosyn Against Gram-Positive Bacteria

• MRSA: Zosyn may not be effective against MRSA, and its use in combination with vancomycin may be necessary to achieve synergy 6, 7.
• Vancomycin-resistant enterococci: Zosyn may not be effective against these bacteria, and alternative treatments may be necessary.