Fomepizole side effects: what 189 FDA adverse event reports show

Fomepizole · 12 reaction terms · 179 drug–reaction co-reports · data 2026-09-14

Drug class

Antidote

FDA label (Established Pharmacologic Class) · compare the class

Who reports

189 reports · 98% serious · 69 with death outcome · 43% female

openFDA FAERS counts, all years, deduplication not applied

Used for

Fomepizole injection is indicated as an antidote for ethylene glycol (such as antifreeze) or methanol poisoning, or for use in suspected ethylene glycol or methanol ingestion, either alone or in combination with hemodialysis (see DOSAGE AND ADMINISTRATION ).

FDA label, Indications and Usage

What it is

DESCRIPTION Fomepizole Injection is intended for intravenous use. Fomepizole Injection is a competitive inhibitor of alcohol dehydrogenase.

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 10 strongest signals

Reporting / coding artifact 1Not in label — unassessed 9

What the badges mean

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. 2 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
Brain oedema	16	140.7 88.0–225.0ROR 153.7 · χ² 2,081 / p <1e-300	120.7 EB05 78.8 · IC025 +3.9 3/3 methods agree	Not in label — unassessed	serious PRR 83.0	no trial data cached
Hepatotoxicity (liver damage)	17	85.1 54.1–134.0ROR 93.5 · χ² 1,331 / p 9e-292	77.9 EB05 51.5 · IC025 +3.8 3/3 methods agree	Not in label — unassessed	serious PRR 50.8	no trial data cached
Acute hepatic failure	10	81.6 44.7–149.3ROR 86.1 · χ² 718 / p 2e-158	71.0 EB05 41.2 · IC025 +3.0 3/3 methods agree	Not in label — unassessed	serious PRR 47.7	no trial data cached
Metabolic acidosis	23	80.7 55.0–118.3ROR 91.7 · χ² 1,732 / p <1e-300	75.7 EB05 53.1 · IC025 +4.2 3/3 methods agree	Not in label — unassessed	serious PRR 47.4 · 95% clinician	no trial data cached
Coagulopathy	10	66.8 36.5–122.1ROR 70.5 · χ² 584 / p 2e-129	59.6 EB05 34.6 · IC025 +2.9 3/3 methods agree	Not in label — unassessed	serious PRR 40.8	no trial data cached
Encephalopathy	12	54.4 31.4–94.0ROR 58.0 · χ² 577 / p 9e-128	50.3 EB05 30.6 · IC025 +3.1 3/3 methods agree	Not in label — unassessed	serious PRR 31.9	no trial data cached
Respiratory depression	5	45.3 19.1–107.5ROR 46.5 · χ² 174 / p 4e-40	38.5 EB05 17.1 · IC025 +1.6 3/3 methods agree	Not in label — unassessed	serious PRR 27.2	no trial data cached
Lactic acidosis	11	38.0 21.4–67.5ROR 40.3 · χ² 361 / p 9e-81	35.9 EB05 21.3 · IC025 +2.8 3/3 methods agree	Not in label — unassessed	serious PRR 22.3	no trial data cached
Toxicity to various agents	50	33.1 26.1–41.9ROR 44.6 · χ² 1,535 / p <1e-300	32.7 EB05 25.8 · IC025 +4.2 3/3 methods agree	Not in label — unassessed	serious PRR 19.9 · 98% clinician	no trial data cached
Intentional overdose	18	31.3 20.2–48.6ROR 34.5 · χ² 500 / p 5e-111	30.4 EB05 20.3 · IC025 +3.3 3/3 methods agree	Reporting / coding artifact	serious PRR 19.0	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
Toxicity to various agents	50	33.1 26.1–41.9ROR 44.6 · χ² 1,535 / p <1e-300	32.7 EB05 25.8 · IC025 +4.2 3/3 methods agree	Not in label — unassessed	serious PRR 19.9 · 98% clinician	no trial data cached
Metabolic acidosis	23	80.7 55.0–118.3ROR 91.7 · χ² 1,732 / p <1e-300	75.7 EB05 53.1 · IC025 +4.2 3/3 methods agree	Not in label — unassessed	serious PRR 47.4 · 95% clinician	no trial data cached
Intentional overdose	18	31.3 20.2–48.6ROR 34.5 · χ² 500 / p 5e-111	30.4 EB05 20.3 · IC025 +3.3 3/3 methods agree	Reporting / coding artifact	serious PRR 19.0	no trial data cached
Hepatotoxicity (liver damage)	17	85.1 54.1–134.0ROR 93.5 · χ² 1,331 / p 9e-292	77.9 EB05 51.5 · IC025 +3.8 3/3 methods agree	Not in label — unassessed	serious PRR 50.8	no trial data cached
Brain oedema	16	140.7 88.0–225.0ROR 153.7 · χ² 2,081 / p <1e-300	120.7 EB05 78.8 · IC025 +3.9 3/3 methods agree	Not in label — unassessed	serious PRR 83.0	no trial data cached
Encephalopathy	12	54.4 31.4–94.0ROR 58.0 · χ² 577 / p 9e-128	50.3 EB05 30.6 · IC025 +3.1 3/3 methods agree	Not in label — unassessed	serious PRR 31.9	no trial data cached
Lactic acidosis	11	38.0 21.4–67.5ROR 40.3 · χ² 361 / p 9e-81	35.9 EB05 21.3 · IC025 +2.8 3/3 methods agree	Not in label — unassessed	serious PRR 22.3	no trial data cached
Coagulopathy	10	66.8 36.5–122.1ROR 70.5 · χ² 584 / p 2e-129	59.6 EB05 34.6 · IC025 +2.9 3/3 methods agree	Not in label — unassessed	serious PRR 40.8	no trial data cached
Acute hepatic failure	10	81.6 44.7–149.3ROR 86.1 · χ² 718 / p 2e-158	71.0 EB05 41.2 · IC025 +3.0 3/3 methods agree	Not in label — unassessed	serious PRR 47.7	no trial data cached
Respiratory depression	5	45.3 19.1–107.5ROR 46.5 · χ² 174 / p 4e-40	38.5 EB05 17.1 · IC025 +1.6 3/3 methods agree	Not in label — unassessed	serious PRR 27.2	no trial data cached
Hypothermia	4	43.8 16.6–115.4ROR 44.7 · χ² 127 / p 9e-30	35.2 EB05 12.6 · IC025 +1.2 3/3 methods agree	Not in label — unassessed	serious PRR 26.0	no trial data cached
Drug toxicity	3	24.1 7.8–74.1ROR 24.5 · χ² 45 / p 8e-12	14.7 EB05 3.1 · IC025 +0.4 3/3 methods agree	Not in label — unassessed	serious PRR 14.7	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.

Metabolic acidosis — n=23, PRR 80.7
Toxicity to various agents — n=50, PRR 33.1

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 Fomepizole?

In FDA FAERS, the most frequently co-reported reaction terms for Fomepizole are toxicity to various agents, metabolic acidosis, hepatotoxicity, brain oedema, encephalopathy, lactic acidosis. 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 Fomepizole have an FDA boxed warning?

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

Do FAERS signals prove that Fomepizole 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 1dea37fd-ec17-416e-b28e-980a87d49e1a, effective 20231026; matched on openfda.generic_name.exact:"FOMEPIZOLE")
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, 12 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.