ampicillin/sulbactam vs piperacillin/tazobactam
Side-by-side comparison of ampicillin/sulbactam and piperacillin/tazobactam Data from FDA drug databases (Orange Book, NDC Directory, recalls, shortages) covering 20,000+ approved drugs, plus CMS pricing; see our methodology.
Unasyn
Zosyn
Unasyn is a combination of two antibiotics that fights bacteria in your body. It contains ampicillin and sulbactam.
Zosyn is a combination of two medicines, piperacillin and tazobactam. It is an antibiotic that fights bacterial infections.
Unasyn treats skin infections, infections in the stomach area, and infections in women's reproductive organs. It is used when these infections are caused by certain types of bacteria. Your doctor will test to make sure Unasyn is the right medicine for your infection.
Zosyn treats several types of infections caused by bacteria. It can treat infections in the stomach area for adults and kids 2 months and older. It can also treat pneumonia that starts in the hospital for adults and kids 2 months and older. In adults, Zosyn can treat skin infections, infections in the female pelvis, and pneumonia that starts outside the hospital.
Ampicillin kills bacteria. Sulbactam helps ampicillin work better by preventing bacteria from breaking down ampicillin. Together, they stop the growth of bacteria.
Piperacillin kills bacteria. Tazobactam helps piperacillin work better by blocking enzymes that can break down piperacillin. This allows piperacillin to effectively fight the infection.
- • Pain at the injection site
- • Diarrhea
- • Rash
- • Diarrhea
- • Constipation
- • Nausea
- • Headache
- • Trouble sleeping
- Drug Ineffective 77
- Pyrexia 71
- Off Label Use 44
- Pneumonia 44
- Condition Aggravated 37
- Drug Ineffective 1,390
- Off Label Use 988
- Acute Kidney Injury 915
- Pyrexia 869
- Thrombocytopenia 471
You should not take Unasyn if you have had a severe allergic reaction to penicillins or cephalosporins. You should also not take it if you have had liver problems caused by Unasyn in the past.
Zosyn can cause severe allergic reactions. Tell your doctor right away if you have a rash or trouble breathing. Zosyn can also cause severe skin reactions, blood problems, seizures, kidney problems, and severe diarrhea. If you have any of these, contact your doctor immediately.
Tell your doctor if you are pregnant or plan to become pregnant. It is not known if Unasyn will harm your unborn baby. Talk to your doctor about the risks and benefits of taking Unasyn while breastfeeding.
Tell your doctor if you are pregnant or plan to become pregnant. It is not known if Zosyn will harm your unborn baby. Talk to your doctor about the risks and benefits of using Zosyn during pregnancy. It is also not known if Zosyn passes into breast milk.
How to Read This ampicillin/sulbactam vs piperacillin/tazobactam Comparison
ampicillin/sulbactam is classified in the Penicillin / Beta-Lactamase Inhibitor drug class, while piperacillin/tazobactam sits within the Penicillin / Beta-Lactamase Inhibitor class. Because both drugs share the same classification, they are often considered interchangeable in theory — but clinical outcomes rarely track that cleanly. Both drugs are prescription-only, so a licensed provider must authorize use.
Adverse event totals above are pulled from the FDA's Adverse Event Reporting System (FAERS). For these top-ranked reactions alone, ampicillin/sulbactam has 273 submissions while piperacillin/tazobactam has 4,633. Those figures reflect cumulative reporting volume — not per-patient risk — so older, widely dispensed drugs typically look worse on count alone. No direct interaction between these two drugs is listed in our FDA-derived dataset, though co-prescription still warrants pharmacist review. Serious warnings, pregnancy guidance, and contraindications can differ even when indications overlap.
A table cannot substitute for clinical judgment. Effectiveness, tolerability, drug-drug interactions with your other medications, kidney and liver function, pregnancy status, insurance formulary, and price all feed into a decision that only a licensed prescriber can make responsibly. Data here is sourced from FDA Structured Product Labels (SPL) and FAERS, both of which update as manufacturers and clinicians submit new information. This page is for educational purposes only, is not medical advice, and should not be used to self-switch between ampicillin/sulbactam and piperacillin/tazobactam — always consult your physician or pharmacist first.
Important: This comparison is for informational purposes only. Drug effects vary between individuals. Always consult your doctor or pharmacist for personalized medical advice.