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

From the Guidelines

Yes, Zosyn (piperacillin-tazobactam) does cover gram-positive bacilli. Zosyn is a combination antibiotic consisting of piperacillin, an extended-spectrum penicillin, and tazobactam, a beta-lactamase inhibitor. This combination provides broad-spectrum coverage against many bacterial pathogens. For gram-positive bacilli specifically, Zosyn is effective against organisms such as Listeria monocytogenes and many Clostridium species, as seen in the treatment of necrotizing soft tissue infections 1. It also covers many gram-positive cocci including streptococci and methicillin-susceptible Staphylococcus aureus (MSSA). The typical dosing for adults with normal renal function is 3.375g or 4.5g IV every 6 hours, with adjustments needed for patients with renal impairment. Zosyn works by inhibiting bacterial cell wall synthesis, and the addition of tazobactam extends its spectrum by protecting piperacillin from degradation by certain beta-lactamase enzymes. However, it's essential to note that Zosyn does not cover methicillin-resistant Staphylococcus aureus (MRSA) or Enterococcus faecium, so additional coverage may be needed if these pathogens are suspected, as recommended in guidelines for managing anorectal emergencies 1 and infective endocarditis 1.

Some key points to consider when using Zosyn include:

• Its effectiveness against a wide range of gram-positive and gram-negative bacteria, including those causing skin and soft tissue infections 1.
• The importance of adjusting the dose in patients with renal impairment to avoid toxicity.
• The need for additional coverage against MRSA and Enterococcus faecium, which are not covered by Zosyn, as highlighted in various guidelines 1.
• The use of Zosyn in combination with other antibiotics for the treatment of complex infections, such as those involving multiple organisms or resistant strains 1.

In clinical practice, the choice of antibiotic should always be guided by the most recent and highest quality evidence available, taking into account local resistance patterns and the specific needs of the patient, as emphasized in the 2024 guidelines on essential medicines and aware recommendations on first- and second-choice antibiotics for empiric treatment of clinical infections 1.

From the FDA Drug Label

Piperacillin and tazobactam has been shown to be active against most isolates of the following microorganisms, both in vitro and in clinical infections 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†

The answer to whether Zosyn (piperacillin/tazobactam) covers Gram-positive bacilli is not directly stated in the provided text. However, based on the information provided, Zosyn is active 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

But it does not explicitly mention coverage of Gram-positive bacilli. Therefore, a conservative clinical decision would be to not assume coverage of Gram-positive bacilli without further information. 2

From the Research

Antibacterial Activity of Zosyn

• Zosyn, also known as piperacillin/tazobactam, has a broad spectrum of antibacterial activity that includes Gram-positive and Gram-negative aerobic and anaerobic bacteria 3, 4, 5.
• The combination of piperacillin and tazobactam enhances the antimicrobial activity against Gram-positive, Gram-negative, and anaerobic bacteria 5.
• Zosyn is effective against many pathogens producing beta-lactamases, including oxacillin-susceptible Staphylococcus spp., Bacillus spp., and vancomycin-susceptible enterococci 6.

Coverage of Gram-Positive Bacilli

• Zosyn has been shown to be active against Gram-positive bacilli, including Streptococcus spp. and Corynebacterium spp. 6.
• The susceptibility rates of Zosyn against Gram-positive bacilli are high, with 100.0% susceptibility against oxacillin-susceptible Staphylococcus spp. and 91.7% susceptibility against Bacillus spp. 6.
• However, the activity of Zosyn against Gram-positive bacilli that produce beta-lactamases, such as methicillin-resistant Staphylococcus aureus (MRSA), is limited 6.

Clinical Efficacy

• Zosyn has been shown to be clinically effective in the treatment of various infections, including lower respiratory tract infections, intra-abdominal infections, skin and soft tissue infections, and febrile neutropenia 3, 4, 7.
• Zosyn has been compared to other antibacterial regimens in clinical trials and has shown higher clinical success rates, particularly in the treatment of patients with intra-abdominal infections and febrile neutropenia 4, 7.