Zafirlukast side effects: what 880 FDA adverse event reports show

Zafirlukast · 21 reaction terms · 400 drug–reaction co-reports · data 2026-09-14

Drug class

Leukotriene Receptor Antagonist

FDA label (Established Pharmacologic Class)

Who reports

880 reports · 53% serious · 43 with death outcome · 72% female

openFDA FAERS counts, all years, deduplication not applied

Used for

Zafirlukast is indicated for the prophylaxis and chronic treatment of asthma in adults and children 5 years of age and older.

FDA label, Indications and Usage

What it is

DESCRIPTION Zafirlukast is a synthetic, selective peptide leukotriene receptor antagonist (LTRA), with the chemical name 4-(5-cyclopentyloxy-carbonylamino-1-methyl-indol-3-ylmethyl)-3-methoxy-N-o-tolylsulfonylbenzamide.

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 15 strongest signals

Labeled (related wording) 1Likely indication confounding 1Not in label — unassessed 13

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.
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. 6 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
Sputum discoloured	23	58.0 38.8–86.9ROR 59.6 · χ² 1,231 / p 7e-270	55.4 EB05 38.9 · IC025 +4.0 3/3 methods agree	Not in label — unassessed	serious PRR 82.5 · ♀ 0% (drug 72%)	no trial data cached
Emphysema	19	44.8 28.7–69.9ROR 45.7 · χ² 769 / p 2e-169	42.9 EB05 29.0 · IC025 +3.6 3/3 methods agree	Not in label — unassessed	serious PRR 55.0	no trial data cached
Aphonia	22	37.6 24.9–56.8ROR 38.5 · χ² 747 / p 1e-164	36.5 EB05 25.4 · IC025 +3.7 3/3 methods agree	Not in label — unassessed	serious PRR 69.2 · ♀ 10% (drug 72%)	no trial data cached
Pulmonary mass	23	36.9 24.6–55.2ROR 37.8 · χ² 766 / p 5e-169	35.8 EB05 25.1 · IC025 +3.7 3/3 methods agree	Not in label — unassessed	serious PRR 43.7 · ♀ 18% (drug 72%)	no trial data cached
Hiatus hernia	19	34.9 22.4–54.5ROR 35.7 · χ² 592 / p 5e-131	33.8 EB05 22.9 · IC025 +3.5 3/3 methods agree	Not in label — unassessed	serious PRR 43.1	no trial data cached
Impaired quality of life	14	23.2 13.8–39.0ROR 23.5 · χ² 275 / p 4e-62	22.4 EB05 14.0 · IC025 +2.8 3/3 methods agree	Not in label — unassessed	serious PRR 21.4	no trial data cached
Asthma	94	20.0 16.5–24.2ROR 22.2 · χ² 1,683 / p <1e-300	19.9 EB05 16.7 · IC025 +3.8 3/3 methods agree	Likely indication confounding term in indications; also in warnings	serious PRR 20.5	no trial data cached
Dyspnoea exertional	31	19.7 13.9–27.8ROR 20.4 · χ² 531 / p 7e-118	19.4 EB05 14.3 · IC025 +3.3 3/3 methods agree	Not in label — unassessed	serious PRR 26.1 · ♀ 23% (drug 72%)	no trial data cached
Wheezing	47	18.9 14.3–25.0ROR 19.9 · χ² 782 / p 3e-172	18.8 EB05 14.7 · IC025 +3.5 3/3 methods agree	Not in label — unassessed	serious PRR 22.3 · ♀ 39% (drug 72%)	no trial data cached
Seasonal allergy	10	16.9 9.1–31.3ROR 17.1 · χ² 134 / p 3e-31	15.4 EB05 7.8 · IC025 +2.2 3/3 methods agree	Not in label — unassessed	serious n=5	no trial data cached
Respiratory disorder	21	16.7 10.9–25.4ROR 17.1 · χ² 294 / p 3e-66	16.2 EB05 10.9 · IC025 +2.9 3/3 methods agree	Labeled (related wording) related wording	serious PRR 22.5 · ♀ 10% (drug 72%)	no trial data cached
Productive cough (cough with phlegm)	31	15.6 11.0–22.0ROR 16.1 · χ² 410 / p 2e-91	15.3 EB05 11.1 · IC025 +3.1 3/3 methods agree	Not in label — unassessed	serious PRR 21.2 · ♀ 23% (drug 72%)	no trial data cached
Nerve compression	5	12.9 5.4–31.0ROR 13.0 · χ² 44 / p 2e-11	8.6 EB05 3.2 · IC025 +1.1 3/3 methods agree	Not in label — unassessed	serious PRR 19.0	no trial data cached
Sleep disorder due to a general medical condition	5	7.4 3.1–17.6ROR 7.4 · χ² 21 / p 2e-6	4.8 EB05 2.2 · IC025 +0.7 3/3 methods agree	Not in label — unassessed	serious PRR 6.3	no trial data cached
Dermatitis atopic	13	6.2 3.6–10.6ROR 6.3 · χ² 52 / p 3e-13	5.2 EB05 3.2 · IC025 +1.4 3/3 methods agree	Not in label — unassessed	serious n=3	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	94	20.0 16.5–24.2ROR 22.2 · χ² 1,683 / p <1e-300	19.9 EB05 16.7 · IC025 +3.8 3/3 methods agree	Likely indication confounding term in indications; also in warnings	serious PRR 20.5	no trial data cached
Wheezing	47	18.9 14.3–25.0ROR 19.9 · χ² 782 / p 3e-172	18.8 EB05 14.7 · IC025 +3.5 3/3 methods agree	Not in label — unassessed	serious PRR 22.3 · ♀ 39% (drug 72%)	no trial data cached
Productive cough (cough with phlegm)	31	15.6 11.0–22.0ROR 16.1 · χ² 410 / p 2e-91	15.3 EB05 11.1 · IC025 +3.1 3/3 methods agree	Not in label — unassessed	serious PRR 21.2 · ♀ 23% (drug 72%)	no trial data cached
Dyspnoea exertional	31	19.7 13.9–27.8ROR 20.4 · χ² 531 / p 7e-118	19.4 EB05 14.3 · IC025 +3.3 3/3 methods agree	Not in label — unassessed	serious PRR 26.1 · ♀ 23% (drug 72%)	no trial data cached
Pulmonary mass	23	36.9 24.6–55.2ROR 37.8 · χ² 766 / p 5e-169	35.8 EB05 25.1 · IC025 +3.7 3/3 methods agree	Not in label — unassessed	serious PRR 43.7 · ♀ 18% (drug 72%)	no trial data cached
Sputum discoloured	23	58.0 38.8–86.9ROR 59.6 · χ² 1,231 / p 7e-270	55.4 EB05 38.9 · IC025 +4.0 3/3 methods agree	Not in label — unassessed	serious PRR 82.5 · ♀ 0% (drug 72%)	no trial data cached
Aphonia	22	37.6 24.9–56.8ROR 38.5 · χ² 747 / p 1e-164	36.5 EB05 25.4 · IC025 +3.7 3/3 methods agree	Not in label — unassessed	serious PRR 69.2 · ♀ 10% (drug 72%)	no trial data cached
Respiratory disorder	21	16.7 10.9–25.4ROR 17.1 · χ² 294 / p 3e-66	16.2 EB05 10.9 · IC025 +2.9 3/3 methods agree	Labeled (related wording) related wording	serious PRR 22.5 · ♀ 10% (drug 72%)	no trial data cached
Hiatus hernia	19	34.9 22.4–54.5ROR 35.7 · χ² 592 / p 5e-131	33.8 EB05 22.9 · IC025 +3.5 3/3 methods agree	Not in label — unassessed	serious PRR 43.1	no trial data cached
Emphysema	19	44.8 28.7–69.9ROR 45.7 · χ² 769 / p 2e-169	42.9 EB05 29.0 · IC025 +3.6 3/3 methods agree	Not in label — unassessed	serious PRR 55.0	no trial data cached
Impaired quality of life	14	23.2 13.8–39.0ROR 23.5 · χ² 275 / p 4e-62	22.4 EB05 14.0 · IC025 +2.8 3/3 methods agree	Not in label — unassessed	serious PRR 21.4	no trial data cached
Dermatitis atopic	13	6.2 3.6–10.6ROR 6.3 · χ² 52 / p 3e-13	5.2 EB05 3.2 · IC025 +1.4 3/3 methods agree	Not in label — unassessed	serious n=3	no trial data cached
Seasonal allergy	10	16.9 9.1–31.3ROR 17.1 · χ² 134 / p 3e-31	15.4 EB05 7.8 · IC025 +2.2 3/3 methods agree	Not in label — unassessed	serious n=5	no trial data cached
Sleep disorder due to a general medical condition	5	7.4 3.1–17.6ROR 7.4 · χ² 21 / p 2e-6	4.8 EB05 2.2 · IC025 +0.7 3/3 methods agree	Not in label — unassessed	serious PRR 6.3	no trial data cached
Nerve compression	5	12.9 5.4–31.0ROR 13.0 · χ² 44 / p 2e-11	8.6 EB05 3.2 · IC025 +1.1 3/3 methods agree	Not in label — unassessed	serious PRR 19.0	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.

Sputum discoloured — n=23, PRR 58.0
Aphonia — n=22, PRR 37.6
Pulmonary mass — n=23, PRR 36.9
Dyspnoea exertional — n=31, PRR 19.7
Wheezing — n=47, PRR 18.9
Productive cough — n=31, PRR 15.6

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 Zafirlukast?

In FDA FAERS, the most frequently co-reported reaction terms for Zafirlukast are asthma, wheezing, productive cough, dyspnoea exertional, pulmonary mass, sputum discoloured. 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 Zafirlukast have an FDA boxed warning?

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

Do FAERS signals prove that Zafirlukast 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 baba507f-6557-4551-815c-9ab6606e4ee1, effective 20260316; matched on openfda.generic_name.exact:"ZAFIRLUKAST")
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, 21 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.