Flecainide Acetate side effects: what 5,244 FDA adverse event reports show
Drug class
Not stated in label
Label matched
Flecainide Acetate (Flecainide Acetate)
Who reports
5,244 reports · 74% serious · 446 with death outcome · 58% female
Used for
In patients without structural heart disease, Flecainide Acetate Tablets USP are indicated for the prevention of: • paroxysmal supraventricular tachycardias (PSVT), including atrioventricular nodal reentrant tachycardia, atrioventricular reentrant tach.
What it is
DESCRIPTION Flecainide acetate is an antiarrhythmic drug available in tablets of 50 mg, 100 mg, or 150 mg for oral administration. Flecainide acetate is benzamide, N-(2-piperidinylmethyl)-2,5-bis (2,2,2-trifluoroethoxy)- monoacetate.
Boxed warning
Mortality Flecainide acetate was included in the National Heart Lung and Blood Institute's Cardiac Arrhythmia Suppression Trial (CAST), a long-term, multicenter, randomized, double-blind study in patients with asymptomatic non-life-threatening ventricular arrhythmias who had a myocardial infarction more than six days but less than two years previously.
Causality screen of the 40 strongest signals
What the badges mean
- Labeled — boxed warning The term (or its clinical synonym) appears in the FDA boxed warning: causality is regulator-recognised and considered serious.
- Labeled adverse reaction The exact term appears in the label's warnings or adverse-reactions sections: a known, expected effect. The FAERS signal confirms the label rather than discovering anything.
- 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.
- Lab value / disease marker A laboratory result, investigation or disease-activity marker (antibody positive, CRP abnormal, swollen joint count) not described in the label. These usually mirror the monitored disease or testing protocol rather than a drug effect; not screened further.
- 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. 343 further terms are in the interactive explorer. Reaction links open the term's cross-drug page.
| Reaction | Reports | PRR 95% CI · ROR · χ²/p | EBGM EB05 · IC025 | Label screen | Serious-only & strata | Trial cross-check |
|---|---|---|---|---|---|---|
| Ventricular tachycardia | 96 | 23.3 19.1–28.4ROR 23.7 · χ² 2,015 / p <1e-300 | 23.1 EB05 19.4 · IC025 +4.0 3/3 methods agree | Labeled — boxed warning exact term | serious PRR 18.0 · 92% clinician | no trial data cached |
| Ventricular extrasystoles | 41 | 15.8 11.7–21.5ROR 15.9 · χ² 552 / p 2e-122 | 15.6 EB05 11.9 · IC025 +3.2 3/3 methods agree | Likely indication confounding shares a disease stem with the indications wording | serious PRR 12.6 | no trial data cached |
| Atrial fibrillation | 350 | 14.4 13.0–15.9ROR 15.4 · χ² 4,354 / p <1e-300 | 14.3 EB05 13.1 · IC025 +3.6 3/3 methods agree | Labeled — boxed warning exact term | serious PRR 11.1 | no trial data cached |
| Sinus bradycardia | 30 | 12.4 8.7–17.8ROR 12.5 · χ² 303 / p 4e-68 | 11.9 EB05 8.5 · IC025 +2.8 3/3 methods agree | Labeled adverse reaction exact term | serious PRR 9.9 | no trial data cached |
| Cardiogenic shock | 41 | 11.5 8.5–15.6ROR 11.6 · χ² 382 / p 2e-85 | 11.1 EB05 8.3 · IC025 +2.8 3/3 methods agree | Labeled adverse reaction exact term | serious PRR 8.9 · 100% clinician | no trial data cached |
| Supraventricular tachycardia | 25 | 10.5 7.1–15.5ROR 10.5 · χ² 204 / p 1e-46 | 9.7 EB05 6.6 · IC025 +2.5 3/3 methods agree | Likely indication confounding term in indications; also in warnings | serious PRR 8.2 · 90% clinician | no trial data cached |
| Electrocardiogram qt prolonged | 88 | 9.8 8.0–12.1ROR 9.9 · χ² 686 / p 2e-151 | 9.6 EB05 7.9 · IC025 +2.9 3/3 methods agree | Labeled (related wording) related wording | serious PRR 7.7 · 96% clinician | no trial data cached |
| Heart rate irregular | 52 | 9.2 7.0–12.0ROR 9.2 · χ² 370 / p 1e-82 | 8.7 EB05 6.8 · IC025 +2.6 3/3 methods agree | Not in label — unassessed | serious PRR 6.5 | no trial data cached |
| Drug toxicity | 30 | 8.7 6.1–12.4ROR 8.7 · χ² 196 / p 6e-45 | 8.0 EB05 5.7 · IC025 +2.3 3/3 methods agree | Not in label — unassessed | serious PRR 7.0 | no trial data cached |
| Bradycardia (slow heart rate) | 115 | 8.7 7.2–10.4ROR 8.8 · χ² 773 / p 2e-170 | 8.5 EB05 7.2 · IC025 +2.8 3/3 methods agree | Labeled adverse reaction exact term | serious PRR 6.8 · 92% clinician | no trial data cached |
| Arrhythmia | 99 | 8.3 6.9–10.1ROR 8.5 · χ² 632 / p 9e-140 | 8.1 EB05 6.8 · IC025 +2.7 3/3 methods agree | Labeled — boxed warning exact term | serious PRR 6.5 | no trial data cached |
| Ventricular fibrillation | 22 | 7.9 5.2–12.0ROR 7.9 · χ² 126 / p 2e-29 | 7.0 EB05 4.8 · IC025 +2.1 3/3 methods agree | Labeled — boxed warning exact term | serious PRR 6.1 | no trial data cached |
| International normalised ratio increased | 56 | 7.8 6.0–10.1ROR 7.9 · χ² 324 / p 8e-73 | 7.4 EB05 5.9 · IC025 +2.4 3/3 methods agree | Lab value / disease marker | serious PRR 6.3 | no trial data cached |
| Mitral valve incompetence | 22 | 7.8 5.1–11.8ROR 7.8 · χ² 123 / p 6e-29 | 6.9 EB05 4.7 · IC025 +2.0 3/3 methods agree | Not in label — unassessed | serious PRR 6.1 | no trial data cached |
| Cholestasis (bile flow blockage) | 37 | 7.8 5.6–10.7ROR 7.8 · χ² 211 / p 4e-48 | 7.2 EB05 5.4 · IC025 +2.3 3/3 methods agree | Labeled adverse reaction exact term | serious PRR 6.1 · 94% clinician | no trial data cached |
| Seasonal allergy | 25 | 7.1 4.8–10.5ROR 7.1 · χ² 125 / p 3e-29 | 6.4 EB05 4.5 · IC025 +2.0 3/3 methods agree | Not in label — unassessed | serious n=12 · 80% consumer | no trial data cached |
| Hypertensive crisis | 19 | 6.8 4.3–10.7ROR 6.8 · χ² 88 / p 3e-21 | 6.0 EB05 4.0 · IC025 +1.8 3/3 methods agree | Not in label — unassessed | serious PRR 5.3 | no trial data cached |
| Hyponatraemia (low sodium) | 94 | 6.7 5.5–8.2ROR 6.8 · χ² 450 / p 3e-100 | 6.5 EB05 5.5 · IC025 +2.4 3/3 methods agree | Not in label — unassessed | serious PRR 5.3 · 96% clinician | no trial data cached |
| Subdural haematoma | 24 | 6.7 4.5–10.0ROR 6.7 · χ² 110 / p 4e-26 | 6.0 EB05 4.2 · IC025 +1.9 3/3 methods agree | Not in label — unassessed | serious PRR 5.0 | no trial data cached |
| Peripheral coldness | 23 | 6.7 4.4–10.0ROR 6.7 · χ² 105 / p 5e-25 | 6.0 EB05 4.2 · IC025 +1.9 3/3 methods agree | Not in label — unassessed | serious PRR 6.5 | no trial data cached |
| Heart rate decreased | 58 | 6.6 5.1–8.5ROR 6.6 · χ² 269 / p 1e-60 | 6.3 EB05 5.0 · IC025 +2.2 3/3 methods agree | Labeled (related wording) related wording | serious PRR 5.6 | no trial data cached |
| Hepatic cytolysis | 17 | 5.6 3.5–9.0ROR 5.6 · χ² 59 / p 7e-15 | 4.9 EB05 3.2 · IC025 +1.5 3/3 methods agree | Not in label — unassessed | serious PRR 4.3 | no trial data cached |
| Haematoma | 34 | 5.2 3.7–7.3ROR 5.3 · χ² 112 / p 2e-26 | 4.9 EB05 3.7 · IC025 +1.7 3/3 methods agree | Not in label — unassessed | serious PRR 4.4 | no trial data cached |
| Blood pressure systolic increased | 25 | 5.1 3.5–7.6ROR 5.1 · χ² 78 / p 4e-19 | 4.7 EB05 3.3 · IC025 +1.6 3/3 methods agree | Lab value / disease marker | serious PRR 3.8 | no trial data cached |
| Gingival bleeding | 17 | 5.0 3.1–8.0ROR 5.0 · χ² 50 / p 7e-13 | 4.4 EB05 2.9 · IC025 +1.3 3/3 methods agree | Not in label — unassessed | serious PRR 4.8 | no trial data cached |
| Basal cell carcinoma | 19 | 4.9 3.1–7.6ROR 4.9 · χ² 55 / p 7e-14 | 4.4 EB05 3.0 · IC025 +1.4 3/3 methods agree | Not in label — unassessed | serious PRR 3.9 | no trial data cached |
| Bladder disorder | 12 | 4.8 2.7–8.5ROR 4.8 · χ² 33 / p 6e-9 | 4.1 EB05 2.5 · IC025 +1.1 3/3 methods agree | Not in label — unassessed | serious n=11 | no trial data cached |
| Osteopenia | 18 | 4.7 3.0–7.5ROR 4.7 · χ² 49 / p 1e-12 | 4.2 EB05 2.9 · IC025 +1.3 3/3 methods agree | Not in label — unassessed | serious PRR 4.1 | no trial data cached |
| Cardio-respiratory arrest | 48 | 4.6 3.4–6.0ROR 4.6 · χ² 130 / p 2e-30 | 4.4 EB05 3.4 · IC025 +1.7 3/3 methods agree | Not in label — unassessed | serious PRR 3.5 · 97% clinician | no trial data cached |
| Cardiac arrest (heart stopping) | 94 | 4.5 3.7–5.5ROR 4.6 · χ² 257 / p 5e-58 | 4.4 EB05 3.7 · IC025 +1.8 3/3 methods agree | Labeled — boxed warning exact term | serious PRR 3.5 · 91% clinician | no trial data cached |
| Interstitial lung disease | 54 | 4.5 3.4–5.8ROR 4.5 · χ² 142 / p 4e-33 | 4.3 EB05 3.4 · IC025 +1.7 3/3 methods agree | Labeled (related wording) related wording | serious PRR 3.5 · ♀ 23% (drug 58%) | no trial data cached |
| Hyperkalaemia (high potassium) | 39 | 4.5 3.3–6.1ROR 4.5 · χ² 102 / p 3e-24 | 4.3 EB05 3.3 · IC025 +1.6 3/3 methods agree | Labeled adverse reaction exact term | serious PRR 3.5 · 91% clinician | no trial data cached |
| Tachycardia (fast heart rate) | 97 | 4.4 3.6–5.3ROR 4.4 · χ² 249 / p 2e-56 | 4.3 EB05 3.6 · IC025 +1.8 3/3 methods agree | Labeled — boxed warning exact term | serious PRR 3.7 | no trial data cached |
| Cerebral haemorrhage | 39 | 4.4 3.2–6.0ROR 4.4 · χ² 98 / p 2e-23 | 4.2 EB05 3.2 · IC025 +1.5 3/3 methods agree | Not in label — unassessed | serious PRR 3.4 | no trial data cached |
| Drug interaction | 172 | 4.3 3.7–5.0ROR 4.5 · χ² 441 / p 3e-98 | 4.3 EB05 3.8 · IC025 +1.8 3/3 methods agree | Reporting / coding artifact | serious PRR 3.5 | no trial data cached |
| Blood thyroid stimulating hormone increased | 10 | 4.3 2.3–8.1ROR 4.3 · χ² 22 / p 1e-6 | 3.7 EB05 2.2 · IC025 +0.8 3/3 methods agree | Lab value / disease marker | serious n=8 | no trial data cached |
| Anorexia | 14 | 4.3 2.5–7.2ROR 4.3 · χ² 32 / p 8e-9 | 3.8 EB05 2.4 · IC025 +1.0 3/3 methods agree | Labeled adverse reaction exact term | serious PRR 4.4 | no trial data cached |
| Hyperbilirubinaemia | 11 | 4.3 2.4–7.7ROR 4.3 · χ² 24 / p 4e-7 | 3.7 EB05 2.2 · IC025 +0.9 3/3 methods agree | Not in label — unassessed | serious PRR 3.4 | no trial data cached |
| Circulatory collapse | 18 | 4.2 2.7–6.7ROR 4.2 · χ² 41 / p 8e-11 | 3.8 EB05 2.6 · IC025 +1.2 3/3 methods agree | Not in label — unassessed | serious PRR 3.3 | no trial data cached |
| Toxicity to various agents | 175 | 4.2 3.6–4.8ROR 4.3 · χ² 422 / p 5e-94 | 4.1 EB05 3.6 · IC025 +1.8 3/3 methods agree | Not in label — unassessed | serious PRR 3.3 · 95% clinician | no trial data cached |
Trial evidence (ClinicalTrials.gov)
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 |
|---|---|---|---|---|---|---|
| Atrial fibrillation | 350 | 14.4 13.0–15.9ROR 15.4 · χ² 4,354 / p <1e-300 | 14.3 EB05 13.1 · IC025 +3.6 3/3 methods agree | Labeled — boxed warning exact term | serious PRR 11.1 | no trial data cached |
| Dyspnoea (shortness of breath) | 283 | 2.0 1.8–2.2ROR 2.1 · χ² 145 / p 1e-33 | 2.0 EB05 1.8 · IC025 +0.8 | Labeled adverse reaction exact term | serious PRR 1.7 | no trial data cached |
| Dizziness | 270 | 2.2 1.9–2.4ROR 2.2 · χ² 173 / p 8e-40 | 2.2 EB05 2.0 · IC025 +0.9 | Labeled adverse reaction exact term | serious PRR 2.0 | no trial data cached |
| Asthenia (weakness) | 203 | 2.2 1.9–2.5ROR 2.2 · χ² 127 / p 8e-30 | 2.2 EB05 1.9 · IC025 +0.9 | Labeled adverse reaction exact term | serious PRR 2.0 | no trial data cached |
| Fall | 190 | 2.3 2.0–2.6ROR 2.3 · χ² 138 / p 3e-32 | 2.3 EB05 2.0 · IC025 +0.9 3/3 methods agree | Not in label — unassessed | serious PRR 1.9 | no trial data cached |
| Hypotension (low blood pressure) | 178 | 3.6 3.1–4.1ROR 3.6 · χ² 327 / p 2e-73 | 3.5 EB05 3.1 · IC025 +1.6 3/3 methods agree | Labeled adverse reaction exact term | serious PRR 2.9 | no trial data cached |
| Toxicity to various agents | 175 | 4.2 3.6–4.8ROR 4.3 · χ² 422 / p 5e-94 | 4.1 EB05 3.6 · IC025 +1.8 3/3 methods agree | Not in label — unassessed | serious PRR 3.3 · 95% clinician | no trial data cached |
| Drug interaction | 172 | 4.3 3.7–5.0ROR 4.5 · χ² 441 / p 3e-98 | 4.3 EB05 3.8 · IC025 +1.8 3/3 methods agree | Reporting / coding artifact | serious PRR 3.5 | no trial data cached |
| Cough | 145 | 2.1 1.8–2.4ROR 2.1 · χ² 80 / p 2e-19 | 2.1 EB05 1.8 · IC025 +0.8 | Not in label — unassessed | serious PRR 1.7 | no trial data cached |
| Bradycardia (slow heart rate) | 115 | 8.7 7.2–10.4ROR 8.8 · χ² 773 / p 2e-170 | 8.5 EB05 7.2 · IC025 +2.8 3/3 methods agree | Labeled adverse reaction exact term | serious PRR 6.8 · 92% clinician | no trial data cached |
| Palpitations (pounding heartbeat) | 108 | 3.7 3.1–4.5ROR 3.7 · χ² 210 / p 6e-48 | 3.6 EB05 3.1 · IC025 +1.5 3/3 methods agree | Not in label — unassessed | serious PRR 3.6 | no trial data cached |
| Syncope (fainting) | 103 | 4.1 3.4–5.0ROR 4.2 · χ² 241 / p 1e-54 | 4.0 EB05 3.4 · IC025 +1.7 3/3 methods agree | Labeled adverse reaction exact term | serious PRR 3.3 | no trial data cached |
| Loss of consciousness | 102 | 3.2 2.6–3.9ROR 3.2 · χ² 151 / p 5e-35 | 3.1 EB05 2.7 · IC025 +1.3 3/3 methods agree | Labeled (related wording) related wording | serious PRR 2.5 | no trial data cached |
| Arrhythmia | 99 | 8.3 6.9–10.1ROR 8.5 · χ² 632 / p 9e-140 | 8.1 EB05 6.8 · IC025 +2.7 3/3 methods agree | Labeled — boxed warning exact term | serious PRR 6.5 | no trial data cached |
| Tachycardia (fast heart rate) | 97 | 4.4 3.6–5.3ROR 4.4 · χ² 249 / p 2e-56 | 4.3 EB05 3.6 · IC025 +1.8 3/3 methods agree | Labeled — boxed warning exact term | serious PRR 3.7 | 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.
- Heart rate irregular — n=52, PRR 9.2
- Drug toxicity — n=30, PRR 8.7
- Mitral valve incompetence — n=22, PRR 7.8
- Seasonal allergy — n=25, PRR 7.1
- Hyponatraemia — n=94, PRR 6.7
- Subdural haematoma — n=24, PRR 6.7
- Peripheral coldness — n=23, PRR 6.7
- Haematoma — n=34, PRR 5.2
- Cardio-respiratory arrest — n=48, PRR 4.6
- Cerebral haemorrhage — n=39, PRR 4.4
✓ A hand-written Bradford Hill causality assessment exists for this drug: Flecainide ↔ Proarrhythmia.
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 Flecainide?
In FDA FAERS, the most frequently co-reported reaction terms for Flecainide are atrial fibrillation, dyspnoea, dizziness, asthenia, fall, hypotension. 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 Flecainide have an FDA boxed warning?
Yes. The current FDA label carries a boxed warning: Mortality Flecainide acetate was included in the National Heart Lung and Blood Institute's Cardiac Arrhythmia Suppression Trial (CAST), a long-term, multicenter, randomized, double-blind study in patients with asymptomatic non-life-threatening ventricular arrhythmias who had a myocardial infarction more than six days but less than two years previously.
Do FAERS signals prove that Flecainide 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 1a2a5e08-2697-4a00-94fe-de07148acbd9, effective 20251126; matched on
openfda.generic_name.exact:"FLECAINIDE ACETATE") - 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, fieldpatient.drug.openfda.generic_name.exact, 383 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.