Is Zosyn (piperacillin/tazobactam) safe during pregnancy?

From the Guidelines

Zosyn (piperacillin-tazobactam) is generally considered safe for use during pregnancy when medically necessary, as supported by the most recent evidence from 2025 1.

Key Points to Consider

• The medication is classified as a Pregnancy Category B medication, meaning animal studies have not shown harm to the fetus, though adequate human studies are limited.
• Doctors may prescribe Zosyn during pregnancy to treat serious bacterial infections when the potential benefits outweigh the risks.
• The typical dosage is 3.375 to 4.5 grams administered intravenously every 6-8 hours, depending on the severity of infection.
• The medication works by inhibiting bacterial cell wall synthesis, with tazobactam preventing bacterial resistance by inhibiting beta-lactamase enzymes.

Important Considerations

• While Zosyn is considered relatively safe, it should only be used during pregnancy under medical supervision.
• As with any medication during pregnancy, healthcare providers will carefully weigh the benefits of treating the infection against any potential risks to the developing baby.
• If you're pregnant and have been prescribed Zosyn, follow your doctor's instructions carefully and report any unusual side effects promptly.

Comparison with Other Antibiotics

• Other antibiotics such as cephalexin, azithromycin, and clindamycin are also considered safe in pregnancy, with no adverse effects reported 1.
• However, Zosyn's safety profile and effectiveness make it a viable option for treating serious bacterial infections during pregnancy.

Final Recommendation

• Zosyn should be used during pregnancy only when medically necessary and under the supervision of a healthcare provider, as supported by the most recent evidence from 2025 1.

From the FDA Drug Label

Piperacillin and tazobactam cross the placenta in humans. However, there are insufficient data with piperacillin and/or tazobactam in pregnant women to inform a drug-associated risk for major birth defects and miscarriage No fetal structural abnormalities were observed in rats or mice when piperacillin and tazobactam was administered intravenously during organogenesis at doses 1 to 2 times and 2 to 3 times the human dose of piperacillin and tazobactam, respectively, based on body-surface area (mg/m2) However, fetotoxicity in the presence of maternal toxicity was observed in developmental toxicity and peri/postnatal studies conducted in rats (intraperitoneal administration prior to mating and throughout gestation or from gestation day 17 through lactation day 21) at doses less than the maximum recommended human daily dose based on body-surface area (mg/m2)

The safety of zosyn (piperacillin/tazobactam) in pregnancy is not well established due to insufficient data in pregnant women.

• Key points:
  • Piperacillin and tazobactam cross the placenta in humans.
  • No fetal structural abnormalities were observed in animal studies.
  • Fetotoxicity was observed in animal studies at certain doses.
• Clinical decision: Piperacillin and tazobactam should be used in pregnancy only if the potential benefit justifies the potential risk to the fetus 2, 2, 2.

From the Research

Safety of Zosyn in Pregnancy

• The use of piperacillin/tazobactam, also known as Zosyn, during pregnancy is considered to be moderately safe (pregnancy category B) for the human embryo-foetus 3.
• However, there have been reported cases of adverse reactions, such as bone marrow suppression, in pregnant women taking Zosyn 3.
• A study found that Zosyn was effective and well-tolerated in patients with various infections, but the incidence of adverse events was higher when the combination was given with an aminoglycoside than when given as monotherapy 4.
• Another study compared the safety and efficacy of Zosyn with ciprofloxacin plus metronidazole in the treatment of complicated intraabdominal infections, and found that Zosyn was clinically effective, but had a higher rate of postsurgical wound infections 5.

Adverse Reactions

• The most common adverse reactions reported with Zosyn are gastrointestinal symptoms, such as diarrhea, and skin reactions 4.
• Haematological reactions, such as leucopenia, neutropenia, and thrombocytopenia, have also been reported, although these are less common (<1%) 3.
• The use of Zosyn during pregnancy has been associated with a probable adverse drug reaction, as determined by the Naranjo Adverse Drug Reaction Probability scales 3.

Reference Guides

• A systematic review and comparative analysis of reference guides for the safe use of drugs during pregnancy found that current reference guides are less scientific and reliable, and there are considerable discrepancies in recommendations from different reference guides concerning drug use during pregnancy 6.
• The review highlighted the need for more comprehensive and evidence-based reference guides to inform the safe use of drugs during pregnancy 6.