Zileuton side effects: what 639 FDA adverse event reports show

Zileuton · 6 reaction terms · 121 drug–reaction co-reports · data 2026-09-14

Drug class

5-Lipoxygenase Inhibitor

FDA label (Established Pharmacologic Class)

Who reports

639 reports · 55% serious · 22 with death outcome · 73% female

openFDA FAERS counts, all years, deduplication not applied

Used for

Zileuton extended-release tablets are indicated for the prophylaxis and chronic treatment of asthma in adults and children 12 years of age and older. Zileuton extended-release tablets are not indicated for use in the reversal of bronchospasm in acute asthma attacks. Therapy with zileuton extended-release tablet can be continued during acute exacerbations of asthma.

FDA label, Indications and Usage

What it is

Zileuton is an orally active inhibitor of 5-lipoxygenase, the enzyme that catalyzes the formation of leukotrienes from arachidonic acid. Zileuton has the chemical name (±)-1-(1-Benzo[b]thien-2.

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 5 strongest signals

Likely indication confounding 1Not in label — unassessed 4

What the badges mean

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.
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. 1 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
Asthma	76	22.2 18.0–27.4ROR 25.0 · χ² 1,524 / p <1e-300	22.1 EB05 18.2 · IC025 +3.9 3/3 methods agree	Likely indication confounding term in indications; also in warnings	serious PRR 23.8	no trial data cached
Pharyngeal swelling	6	20.5 9.2–45.5ROR 20.7 · χ² 93 / p 3e-22	17.4 EB05 6.4 · IC025 +1.6 3/3 methods agree	Not in label — unassessed	serious n=5	no trial data cached
Impaired quality of life	7	15.9 7.6–33.3ROR 16.1 · χ² 84 / p 3e-20	13.1 EB05 5.4 · IC025 +1.7 3/3 methods agree	Not in label — unassessed	serious PRR 7.1	no trial data cached
Pharyngeal oedema	7	14.7 7.0–30.7ROR 14.8 · χ² 76 / p 1e-18	11.8 EB05 4.9 · IC025 +1.6 3/3 methods agree	Not in label — unassessed	serious PRR 20.4	no trial data cached
Anaphylactic reaction (severe allergic reaction)	22	13.1 8.7–19.8ROR 13.5 · χ² 235 / p 3e-53	12.5 EB05 8.2 · IC025 +2.7 3/3 methods agree	Not in label — unassessed	serious PRR 14.1	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
Asthma	76	22.2 18.0–27.4ROR 25.0 · χ² 1,524 / p <1e-300	22.1 EB05 18.2 · IC025 +3.9 3/3 methods agree	Likely indication confounding term in indications; also in warnings	serious PRR 23.8	no trial data cached
Anaphylactic reaction (severe allergic reaction)	22	13.1 8.7–19.8ROR 13.5 · χ² 235 / p 3e-53	12.5 EB05 8.2 · IC025 +2.7 3/3 methods agree	Not in label — unassessed	serious PRR 14.1	no trial data cached
Pharyngeal oedema	7	14.7 7.0–30.7ROR 14.8 · χ² 76 / p 1e-18	11.8 EB05 4.9 · IC025 +1.6 3/3 methods agree	Not in label — unassessed	serious PRR 20.4	no trial data cached
Impaired quality of life	7	15.9 7.6–33.3ROR 16.1 · χ² 84 / p 3e-20	13.1 EB05 5.4 · IC025 +1.7 3/3 methods agree	Not in label — unassessed	serious PRR 7.1	no trial data cached
Pharyngeal swelling	6	20.5 9.2–45.5ROR 20.7 · χ² 93 / p 3e-22	17.4 EB05 6.4 · IC025 +1.6 3/3 methods agree	Not in label — unassessed	serious n=5	no trial data cached
Hereditary angioedema	3	9.3 3.0–28.9ROR 9.4 · χ² 15 / p 6e-5	4.8 EB05 1.7 · IC025 +0.0	Not in label — unassessed	serious PRR 7.8	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.

Anaphylactic reaction — n=22, PRR 13.1

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 Zileuton?

In FDA FAERS, the most frequently co-reported reaction terms for Zileuton are asthma, anaphylactic reaction, pharyngeal oedema, impaired quality of life, pharyngeal swelling, hereditary angioedema. 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 Zileuton have an FDA boxed warning?

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

Do FAERS signals prove that Zileuton 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 94313e24-9534-4b6c-b374-c436c4916303, effective 20221014; matched on openfda.generic_name.exact:"ZILEUTON")
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, 6 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.