Ceftolozane and Tazobactam side effects: what 965 FDA adverse event reports show

Ceftolozane And Tazobactam · Zerbaxa · 23 reaction terms · 459 drug–reaction co-reports · data 2026-09-14

Drug class

Not stated in label

Brand names

Zerbaxa

openFDA label

Who reports

965 reports · 68% serious · 228 with death outcome · 38% female

openFDA FAERS counts, all years, deduplication not applied

Used for

ZERBAXA (ceftolozane and tazobactam) is a combination of ceftolozane, a cephalosporin antibacterial, and tazobactam, a beta-lactamase inhibitor, indicated for the treatment of the following infections caused by designated susceptible microorganisms in adult and pediatric patients (at least 32 weeks gestational age): Complicated Intra-abdominal Infections (cIAI), used in combination with metronidazole.

FDA label, Indications and Usage

What it is

ZERBAXA (ceftolozane and tazobactam) is an antibacterial combination product consisting of the cephalosporin antibacterial drug ceftolozane sulfate and the beta-lactamase inhibitor tazobactam sodium for intravenous administration.

FDA label, Description section

Boxed warning

None in the current label

How to read this page. FAERS is a spontaneous-reporting system: counts are not incidence rates and a signal is not proof of causation. Each reaction below is run through an automated screen — is the term in the FDA label (known), in the indications (the disease being treated), an administrative/coding term, or none of these (unlabeled)? That screen is mechanical text matching, not a causality assessment. The 30 hand-written Bradford Hill assessments are on the causality assessment page. Not medical advice.

Causality screen of the 18 strongest signals

Labeled (related wording) 1Likely indication confounding 1Reporting / coding artifact 5Not in label — unassessed 11

What the badges mean

Labeled (related wording) The label describes this effect under different wording (e.g. 'neutropenia' for 'neutrophil count decreased'). Treated as known.
Likely indication confounding The term appears in the label's indications: reports probably describe the disease being treated (or its progression), not a drug effect. Classic confounding by indication.
Reporting / coding artifact An administrative, monitoring or exposure term (product issue, off-label use, 'test normal', overdose...). Not a biological reaction; a high PRR here reflects how reports are coded.
Not in label — unassessed Not found in the label text, not an artifact pattern. This is a genuine candidate for a formal causality assessment (Bradford Hill / WHO-UMC); it has NOT had one here.

Strongest disproportionality signals

Flagged terms (PRR ≥ 2, χ² ≥ 4, n ≥ 10), ranked by PRR; infinite PRRs (no comparator reports) excluded. The EBGM column is a second, shrinkage-based estimate (MGPS) with its 5th percentile EB05 and the BCPNN IC025; a pair flagged by PRR alone is marked PRR-only and should be read as fragile. The strata column recomputes the PRR on serious reports only and flags pairs whose reports are unusually skewed by sex or come mostly from consumers rather than clinicians. 5 further terms are in the interactive explorer. Reaction links open the term's cross-drug page.

Show: hide coding/lab/outcome terms hide indication terms unlabeled only hide PRR-only

Reaction	Reports	PRR 95% CI · ROR · χ²/p	EBGM EB05 · IC025	Label screen	Serious-only & strata	Trial cross-check
Drug resistance	30	25.4 17.9–36.1ROR 26.2 · χ² 679 / p 5e-150	25.0 EB05 18.4 · IC025 +3.6 3/3 methods agree	Reporting / coding artifact	serious PRR 18.6	no trial data cached
Encephalopathy	23	20.4 13.6–30.6ROR 20.9 · χ² 406 / p 2e-90	20.1 EB05 14.0 · IC025 +3.2 3/3 methods agree	Not in label — unassessed	serious PRR 17.4 · ♀ 67% (drug 38%) · 100% clinician	no trial data cached
Pneumocystis jirovecii pneumonia	9	19.6 10.2–37.5ROR 19.8 · χ² 141 / p 1e-32	18.1 EB05 9.0 · IC025 +2.2 3/3 methods agree	Likely indication confounding shares a disease stem with the indications wording	serious PRR 16.6	no trial data cached
Agranulocytosis (severe loss of white cells)	16	18.8 11.6–30.6ROR 19.1 · χ² 252 / p 4e-57	18.2 EB05 11.6 · IC025 +2.8 3/3 methods agree	Labeled (related wording) related wording	serious PRR 16.0	no trial data cached
Status epilepticus	9	17.3 9.0–33.1ROR 17.4 · χ² 122 / p 1e-28	15.6 EB05 7.4 · IC025 +2.1 3/3 methods agree	Not in label — unassessed	serious PRR 14.7	no trial data cached
Hepatocellular injury	11	16.8 9.3–30.3ROR 17.0 · χ² 148 / p 2e-34	15.6 EB05 8.3 · IC025 +2.3 3/3 methods agree	Not in label — unassessed	serious PRR 14.3	no trial data cached
Generalised tonic-clonic seizure	11	14.6 8.1–26.3ROR 14.8 · χ² 126 / p 1e-29	13.1 EB05 6.8 · IC025 +2.2 3/3 methods agree	Not in label — unassessed	serious PRR 12.6	no trial data cached
Rash maculo-papular	14	13.7 8.2–23.1ROR 13.9 · χ² 153 / p 2e-35	12.6 EB05 7.2 · IC025 +2.4 3/3 methods agree	Not in label — unassessed	serious PRR 12.0	no trial data cached
Septic shock	25	12.6 8.5–18.5ROR 12.9 · χ² 255 / p 9e-58	12.0 EB05 8.2 · IC025 +2.7 3/3 methods agree	Not in label — unassessed	serious PRR 10.7	no trial data cached
Product use in unapproved indication	128	11.4 9.7–13.4ROR 13.0 · χ² 1,216 / p 8e-267	11.3 EB05 9.7 · IC025 +3.2 3/3 methods agree	Reporting / coding artifact	serious PRR 11.2	no trial data cached
No adverse event	89	10.9 8.9–13.3ROR 11.9 · χ² 798 / p 9e-176	10.7 EB05 8.9 · IC025 +3.0 3/3 methods agree	Reporting / coding artifact	serious PRR 3.4 · ♀ 60% (drug 38%)	no trial data cached
Pancytopenia (all blood cells low)	26	10.1 6.9–14.8ROR 10.4 · χ² 206 / p 6e-47	9.4 EB05 6.5 · IC025 +2.5 3/3 methods agree	Not in label — unassessed	serious PRR 8.7 · ♀ 0% (drug 38%) · 100% clinician	no trial data cached
Incorrect product administration duration	8	8.6 4.3–17.1ROR 8.6 · χ² 46 / p 5e-12	6.3 EB05 3.3 · IC025 +1.4 3/3 methods agree	Reporting / coding artifact	serious n=5	no trial data cached
Lymphopenia	5	7.7 3.2–18.5ROR 7.8 · χ² 23 / p 8e-7	5.0 EB05 2.3 · IC025 +0.7 3/3 methods agree	Not in label — unassessed	serious PRR 7.1	no trial data cached
Eosinophilia	6	7.5 3.4–16.6ROR 7.5 · χ² 27 / p 8e-8	5.1 EB05 2.5 · IC025 +0.9 3/3 methods agree	Not in label — unassessed	serious PRR 6.6	no trial data cached
Circumstance or information capable of leading to medication error	10	6.5 3.5–12.0ROR 6.5 · χ² 41 / p 7e-11	5.1 EB05 3.0 · IC025 +1.3 3/3 methods agree	Not in label — unassessed	–	no trial data cached
Drug effective for unapproved indication	8	6.0 3.0–11.9ROR 6.0 · χ² 28 / p 5e-8	4.6 EB05 2.5 · IC025 +1.0 3/3 methods agree	Not in label — unassessed	serious n=5	no trial data cached
Product storage error	15	3.8 2.3–6.2ROR 3.8 · χ² 28 / p 6e-8	3.4 EB05 2.2 · IC025 +0.9 3/3 methods agree	Reporting / coding artifact	serious PRR 4.6	no trial data cached

Trial evidence (ClinicalTrials.gov)

Trial cross-check not yet run for this drug (ClinicalTrials.gov pull covers the 800 most-reported drugs first).

Most frequently reported reactions

By raw co-report count, regardless of disproportionality. Common terms here are often the illness itself or generic outcomes.

Reaction	Reports	PRR 95% CI · ROR · χ²/p	EBGM EB05 · IC025	Label screen	Serious-only & strata	Trial cross-check
Product use in unapproved indication	128	11.4 9.7–13.4ROR 13.0 · χ² 1,216 / p 8e-267	11.3 EB05 9.7 · IC025 +3.2 3/3 methods agree	Reporting / coding artifact	serious PRR 11.2	no trial data cached
No adverse event	89	10.9 8.9–13.3ROR 11.9 · χ² 798 / p 9e-176	10.7 EB05 8.9 · IC025 +3.0 3/3 methods agree	Reporting / coding artifact	serious PRR 3.4 · ♀ 60% (drug 38%)	no trial data cached
Drug resistance	30	25.4 17.9–36.1ROR 26.2 · χ² 679 / p 5e-150	25.0 EB05 18.4 · IC025 +3.6 3/3 methods agree	Reporting / coding artifact	serious PRR 18.6	no trial data cached
Pancytopenia (all blood cells low)	26	10.1 6.9–14.8ROR 10.4 · χ² 206 / p 6e-47	9.4 EB05 6.5 · IC025 +2.5 3/3 methods agree	Not in label — unassessed	serious PRR 8.7 · ♀ 0% (drug 38%) · 100% clinician	no trial data cached
Septic shock	25	12.6 8.5–18.5ROR 12.9 · χ² 255 / p 9e-58	12.0 EB05 8.2 · IC025 +2.7 3/3 methods agree	Not in label — unassessed	serious PRR 10.7	no trial data cached
Encephalopathy	23	20.4 13.6–30.6ROR 20.9 · χ² 406 / p 2e-90	20.1 EB05 14.0 · IC025 +3.2 3/3 methods agree	Not in label — unassessed	serious PRR 17.4 · ♀ 67% (drug 38%) · 100% clinician	no trial data cached
Agranulocytosis (severe loss of white cells)	16	18.8 11.6–30.6ROR 19.1 · χ² 252 / p 4e-57	18.2 EB05 11.6 · IC025 +2.8 3/3 methods agree	Labeled (related wording) related wording	serious PRR 16.0	no trial data cached
Product storage error	15	3.8 2.3–6.2ROR 3.8 · χ² 28 / p 6e-8	3.4 EB05 2.2 · IC025 +0.9 3/3 methods agree	Reporting / coding artifact	serious PRR 4.6	no trial data cached
Rash maculo-papular	14	13.7 8.2–23.1ROR 13.9 · χ² 153 / p 2e-35	12.6 EB05 7.2 · IC025 +2.4 3/3 methods agree	Not in label — unassessed	serious PRR 12.0	no trial data cached
Generalised tonic-clonic seizure	11	14.6 8.1–26.3ROR 14.8 · χ² 126 / p 1e-29	13.1 EB05 6.8 · IC025 +2.2 3/3 methods agree	Not in label — unassessed	serious PRR 12.6	no trial data cached
Hepatocellular injury	11	16.8 9.3–30.3ROR 17.0 · χ² 148 / p 2e-34	15.6 EB05 8.3 · IC025 +2.3 3/3 methods agree	Not in label — unassessed	serious PRR 14.3	no trial data cached
Circumstance or information capable of leading to medication error	10	6.5 3.5–12.0ROR 6.5 · χ² 41 / p 7e-11	5.1 EB05 3.0 · IC025 +1.3 3/3 methods agree	Not in label — unassessed	–	no trial data cached
Status epilepticus	9	17.3 9.0–33.1ROR 17.4 · χ² 122 / p 1e-28	15.6 EB05 7.4 · IC025 +2.1 3/3 methods agree	Not in label — unassessed	serious PRR 14.7	no trial data cached
Pneumocystis jirovecii pneumonia	9	19.6 10.2–37.5ROR 19.8 · χ² 141 / p 1e-32	18.1 EB05 9.0 · IC025 +2.2 3/3 methods agree	Likely indication confounding shares a disease stem with the indications wording	serious PRR 16.6	no trial data cached
Drug effective for unapproved indication	8	6.0 3.0–11.9ROR 6.0 · χ² 28 / p 5e-8	4.6 EB05 2.5 · IC025 +1.0 3/3 methods agree	Not in label — unassessed	serious n=5	no trial data cached

Unlabeled candidate signals

These flagged terms were not found in the FDA label text and do not match an artifact pattern. They are the pairs that would merit a structured assessment (temporality, dose-response, biological plausibility, consistency across databases, trial or cohort evidence). The screen has not done that; string-matching misses label wording, and a strong PRR can still be stimulated reporting, co-medication, or the disease itself.

Encephalopathy — n=23, PRR 20.4
Septic shock — n=25, PRR 12.6
Pancytopenia — n=26, PRR 10.1

Want to assess one of these properly? The runbook describes the Bradford Hill / trial-evidence workflow used on the assessment page, and handoff_top1000_signals.csv lists the strongest unassessed pairs across all drugs.

Common questions

What are the most reported side effects of Ceftolozane and Tazobactam?

In FDA FAERS, the most frequently co-reported reaction terms for Ceftolozane and Tazobactam are pancytopenia, septic shock, encephalopathy, agranulocytosis, rash maculo-papular, generalised tonic-clonic seizure. These are report counts, not rates: FAERS has no denominator, reporting is voluntary and uneven, and a term can be reported because of the illness being treated rather than the drug.

Does Ceftolozane and Tazobactam have an FDA boxed warning?

No. The FDA label retrieved for Ceftolozane and Tazobactam has no boxed warning; see the label's Warnings and Precautions for the recognised risks.

Do FAERS signals prove that Ceftolozane and Tazobactam causes these side effects?

No. A disproportionality signal (PRR, ROR) means a reaction is reported more often with this drug than with others in the database. That can reflect a real effect, but also the disease being treated, stimulated reporting after news or litigation, co-medications, or how reports are coded. Causality needs temporality, dose-response, biological plausibility, consistency across data sources and, ideally, trial or cohort evidence. This page screens each term against the FDA label and ClinicalTrials.gov results; it does not establish causation.

Sources & methods

FDA label via openFDA (set ID 70ac1d90-eff3-4f0b-9f46-5846c571b32f, effective 20260512; matched on openfda.generic_name.exact:"CEFTOLOZANE AND TAZOBACTAM")
Bayesian shrinkage measures computed offline over all 1,317,300 cached pairs: BCPNN information component (IC, with Norén closed-form IC025) and MGPS empirical-Bayes geometric mean (EBGM, EB05) with a two-component gamma prior fitted by maximum marginal likelihood (α₁=0.57, β₁=0.02, α₂=1.42, β₂=0.70, w=0.17); unstratified
FAERS pair statistics from the OpenPV build of 2026-09-14 (openFDA count= aggregation, field patient.drug.openfda.generic_name.exact, 23 reaction terms, min 3 co-reports); PRR/ROR with 95% CI, chi-square with Yates correction
Serious-only and stratified counts (serious:1, patient.patientsex, primarysource.qualification) from openFDA count queries; serious-only PRR uses the drug serious report total and the term global serious total (N_serious=11,882,979); strata shown only when n ≥ 20
Seriousness and sex counts from openFDA count=serious, patient.patientsex, seriousnessdeath

Page generated 2026-10-08. Label and PubChem text are retrieved automatically and may lag the current label; always check the current prescribing information. OpenPV is a beta research tool of the Open Source Medicine Foundation.