Drug · FAERS side-effect profile with label screen
Phenytoin side effects: what 20,744 FDA adverse event reports show
Who reports
20,744 reports · 90% serious · 2,979 with death outcome · 48% female
openFDA FAERS counts, all years, deduplication not applied
Used for
Phenytoin chewable tablets are indicated for the treatment of generalized tonic-clonic (grand mal) and complex partial (psychomotor, temporal lobe) seizures and prevention and treatment of seizures occurring during or following neurosurgery. Phenytoin .
FDA label, Indications and Usage
What it is
Phenytoin is related to the barbiturates in chemical structure, but has a five-membered ring.
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 40 strongest signals
Labeled adverse reaction 4Labeled (related wording) 3Likely indication confounding 1Reporting / coding artifact 3Lab value / disease marker 8Not in label — unassessed 21
What the badges mean
- 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. 1,114 further terms are in the interactive explorer. Reaction links open the term's cross-drug page.
Show:
| Reaction | Reports | PRR 95% CI · ROR · χ²/p | EBGM EB05 · IC025 | Label screen | Serious-only & strata | Trial cross-check |
|---|---|---|---|---|---|---|
| Purple glove syndrome | 65 | 981.4 697.0–1,381.9ROR 984.5 · χ² 31,581 / p <1e-300 | 431.8 EB05 350.6 · IC025 +6.3 3/3 methods agree | Not in label — unassessed | serious n=64 · 100% clinician | not reported in cached trials |
| Inspiratory capacity decreased | 97 | 552.3 431.1–707.6ROR 554.9 · χ² 33,992 / p <1e-300 | 332.4 EB05 280.5 · IC025 +6.6 3/3 methods agree | Not in label — unassessed | serious n=97 · ♀ 0% (drug 48%) · 100% clinician | not reported in cached trials |
| Urine copper increased | 14 | 536.6 280.2–1,027.4ROR 536.9 · χ² 4,522 / p <1e-300 | 236.6 EB05 149.8 · IC025 +3.8 3/3 methods agree | Lab value / disease marker | serious n=14 | not reported in cached trials |
| New onset refractory status epilepticus | 31 | 417.4 274.5–634.8ROR 418.1 · χ² 8,785 / p <1e-300 | 249.3 EB05 184.0 · IC025 +5.1 3/3 methods agree | Not in label — unassessed | serious n=31 · ♀ 0% (drug 48%) · 100% clinician | not reported in cached trials |
| Intra-abdominal pressure increased | 35 | 290.6 199.5–423.4ROR 291.1 · χ² 7,598 / p <1e-300 | 200.7 EB05 150.8 · IC025 +5.2 3/3 methods agree | Lab value / disease marker | serious n=35 · ♀ 100% (drug 48%) | not reported in cached trials |
| Anticonvulsant drug level above therapeutic | 142 | 281.9 234.1–339.4ROR 283.8 · χ² 30,761 / p <1e-300 | 213.6 EB05 185.7 · IC025 +6.7 3/3 methods agree | Lab value / disease marker | serious n=140 · 94% clinician | not reported in cached trials |
| Angiofibroma | 14 | 232.5 130.0–415.9ROR 232.7 · χ² 2,432 / p <1e-300 | 150.4 EB05 95.2 · IC025 +3.8 3/3 methods agree | Not in label — unassessed | serious n=14 | not reported in cached trials |
| Anticonvulsant drug level increased | 298 | 227.0 200.3–257.3ROR 230.3 · χ² 54,436 / p <1e-300 | 182.9 EB05 166.1 · IC025 +7.0 3/3 methods agree | Lab value / disease marker | serious n=271 | not reported in cached trials |
| Anticonvulsant drug level abnormal | 32 | 223.0 152.0–327.1ROR 223.3 · χ² 5,599 / p <1e-300 | 164.6 EB05 122.1 · IC025 +5.0 3/3 methods agree | Lab value / disease marker | serious n=27 | not reported in cached trials |
| Cerebellar atrophy | 144 | 196.8 164.7–235.2ROR 198.2 · χ² 23,267 / p <1e-300 | 161.1 EB05 140.2 · IC025 +6.4 3/3 methods agree | Labeled adverse reaction exact term | serious n=144 · 96% clinician | not reported in cached trials |
| Anti-erythropoietin antibody negative | 14 | 181.2 102.5–320.1ROR 181.3 · χ² 1,973 / p <1e-300 | 127.3 EB05 80.6 · IC025 +3.7 3/3 methods agree | Reporting / coding artifact | serious n=14 | not reported in cached trials |
| Postictal paralysis | 35 | 171.0 119.5–244.6ROR 171.3 · χ² 4,904 / p <1e-300 | 135.4 EB05 101.8 · IC025 +5.0 3/3 methods agree | Not in label — unassessed | serious n=35 | not reported in cached trials |
| Anticonvulsant drug level decreased | 186 | 151.5 130.0–176.7ROR 152.9 · χ² 24,016 / p <1e-300 | 129.9 EB05 115.0 · IC025 +6.4 3/3 methods agree | Lab value / disease marker | serious n=168 | not reported in cached trials |
| Csf oligoclonal band present | 15 | 141.0 82.1–242.1ROR 141.1 · χ² 1,706 / p <1e-300 | 107.2 EB05 68.9 · IC025 +3.8 3/3 methods agree | Lab value / disease marker | serious n=15 | not reported in cached trials |
| Necrosis ischaemic | 54 | 133.5 100.5–177.3ROR 133.9 · χ² 6,147 / p <1e-300 | 113.2 EB05 90.1 · IC025 +5.4 3/3 methods agree | Not in label — unassessed | serious n=54 | not reported in cached trials |
| Multiple-drug resistance | 360 | 133.2 119.4–148.5ROR 135.5 · χ² 41,543 / p <1e-300 | 116.9 EB05 107.1 · IC025 +6.5 3/3 methods agree | Reporting / coding artifact | serious n=289 · 98% clinician | not reported in cached trials |
| Anticonvulsant drug level below therapeutic | 83 | 123.6 98.5–155.2ROR 124.1 · χ² 8,873 / p <1e-300 | 107.4 EB05 89.4 · IC025 +5.7 3/3 methods agree | Lab value / disease marker | serious n=78 | not reported in cached trials |
| Hippocampal sclerosis | 13 | 112.6 63.5–199.9ROR 112.7 · χ² 1,194 / p 6e-262 | 88.5 EB05 55.1 · IC025 +3.5 3/3 methods agree | Not in label — unassessed | serious n=13 | not reported in cached trials |
| Intensive care unit acquired weakness | 36 | 105.2 74.6–148.3ROR 105.4 · χ² 3,267 / p <1e-300 | 90.8 EB05 68.5 · IC025 +4.8 3/3 methods agree | Not in label — unassessed | serious n=36 · ♀ 27% (drug 48%) · 100% clinician | not reported in cached trials |
| Cardiac arrest neonatal | 12 | 95.7 52.9–173.0ROR 95.7 · χ² 941 / p 6e-207 | 77.1 EB05 47.0 · IC025 +3.3 3/3 methods agree | Not in label — unassessed | serious n=12 | not reported in cached trials |
| Bone marrow transplant rejection | 17 | 83.4 50.9–136.9ROR 83.5 · χ² 1,203 / p 7e-264 | 71.2 EB05 47.1 · IC025 +3.8 3/3 methods agree | Not in label — unassessed | serious n=16 | not reported in cached trials |
| Pneumatosis | 33 | 81.0 56.8–115.5ROR 81.1 · χ² 2,338 / p <1e-300 | 72.0 EB05 53.6 · IC025 +4.6 3/3 methods agree | Not in label — unassessed | serious n=33 · ♀ 100% (drug 48%) | not reported in cached trials |
| Congenital aplasia | 21 | 79.0 50.6–123.1ROR 79.0 · χ² 1,426 / p <1e-300 | 68.8 EB05 47.5 · IC025 +4.0 3/3 methods agree | Labeled (related wording) related wording | serious n=21 | not reported in cached trials |
| Status epilepticus | 804 | 77.3 72.0–82.9ROR 80.4 · χ² 56,154 / p <1e-300 | 71.7 EB05 67.6 · IC025 +6.0 3/3 methods agree | Labeled adverse reaction exact term | serious PRR 46.2 · 92% clinician | not reported in cached trials |
| Nystagmus | 359 | 73.3 65.9–81.6ROR 74.6 · χ² 23,797 / p <1e-300 | 68.1 EB05 62.4 · IC025 +5.8 3/3 methods agree | Labeled adverse reaction exact term | serious n=353 · 98% clinician | not reported in cached trials |
| Epileptic encephalopathy | 14 | 68.4 39.8–117.5ROR 68.4 · χ² 808 / p 5e-178 | 59.2 EB05 37.5 · IC025 +3.4 3/3 methods agree | Labeled (related wording) related wording | serious n=14 | not reported in cached trials |
| Sudden unexplained death in epilepsy | 34 | 67.8 47.9–95.9ROR 67.9 · χ² 2,032 / p <1e-300 | 61.4 EB05 46.0 · IC025 +4.5 3/3 methods agree | Not in label — unassessed | serious n=34 · ♀ 0% (drug 48%) | not reported in cached trials |
| Kidney malformation | 21 | 63.0 40.6–97.9ROR 63.1 · χ² 1,148 / p 6e-252 | 56.5 EB05 39.0 · IC025 +3.9 3/3 methods agree | Not in label — unassessed | serious n=21 | not reported in cached trials |
| Propofol infusion syndrome | 41 | 62.3 45.4–85.4ROR 62.4 · χ² 2,269 / p <1e-300 | 57.2 EB05 44.0 · IC025 +4.6 3/3 methods agree | Not in label — unassessed | serious n=41 · 100% clinician | not reported in cached trials |
| Choreoathetosis | 39 | 60.9 44.1–84.1ROR 61.0 · χ² 2,110 / p <1e-300 | 56.0 EB05 42.7 · IC025 +4.5 3/3 methods agree | Not in label — unassessed | serious n=39 · 100% clinician | not reported in cached trials |
| Po2 increased | 29 | 60.7 41.7–88.3ROR 60.8 · χ² 1,549 / p <1e-300 | 55.3 EB05 40.4 · IC025 +4.3 3/3 methods agree | Not in label — unassessed | serious n=29 · ♀ 100% (drug 48%) | not reported in cached trials |
| Gingival hypertrophy | 85 | 60.6 48.7–75.4ROR 60.9 · χ² 4,643 / p <1e-300 | 56.5 EB05 47.1 · IC025 +5.1 3/3 methods agree | Not in label — unassessed | serious n=79 · 92% clinician | not reported in cached trials |
| Vitamin b6 deficiency | 13 | 59.7 34.1–104.5ROR 59.7 · χ² 654 / p 2e-144 | 52.3 EB05 32.5 · IC025 +3.3 3/3 methods agree | Labeled (related wording) related wording | – | not reported in cached trials |
| Renal ischaemia | 30 | 59.1 40.9–85.4ROR 59.2 · χ² 1,563 / p <1e-300 | 54.0 EB05 39.7 · IC025 +4.3 3/3 methods agree | Not in label — unassessed | serious n=30 · ♀ 100% (drug 48%) | not reported in cached trials |
| Craniofacial deformity | 13 | 58.9 33.7–103.0ROR 58.9 · χ² 645 / p 2e-142 | 51.7 EB05 32.1 · IC025 +3.3 3/3 methods agree | Not in label — unassessed | serious n=13 | not reported in cached trials |
| Neurodegenerative disorder | 29 | 50.5 34.8–73.3ROR 50.6 · χ² 1,293 / p 2e-283 | 46.8 EB05 34.1 · IC025 +4.1 3/3 methods agree | Not in label — unassessed | serious n=29 · ♀ 70% (drug 48%) · 100% clinician | not reported in cached trials |
| Partial seizures with secondary generalisation | 21 | 47.3 30.6–73.3ROR 47.4 · χ² 866 / p 1e-190 | 43.6 EB05 30.1 · IC025 +3.7 3/3 methods agree | Likely indication confounding shares a disease stem with the indications wording | serious n=21 · 100% clinician | not reported in cached trials |
| Pco2 increased | 32 | 47.2 33.1–67.2ROR 47.2 · χ² 1,337 / p 5e-293 | 44.0 EB05 32.6 · IC025 +4.2 3/3 methods agree | Not in label — unassessed | serious n=32 · ♀ 100% (drug 48%) | not reported in cached trials |
| Drug level fluctuating | 39 | 46.9 34.0–64.6ROR 47.0 · χ² 1,629 / p <1e-300 | 43.9 EB05 33.5 · IC025 +4.3 3/3 methods agree | Reporting / coding artifact | serious n=27 | not reported in cached trials |
| Ataxia | 527 | 46.7 42.9–51.0ROR 47.9 · χ² 22,504 / p <1e-300 | 44.6 EB05 41.5 · IC025 +5.3 3/3 methods agree | Labeled adverse reaction exact term | serious PRR 30.5 · 97% clinician | not reported in cached trials |
Trial evidence (ClinicalTrials.gov)
✓ Trial adverse-event data found on ClinicalTrials.gov
Largest completed trials with posted results that list Phenytoin as a study intervention. The right-hand column of the signal table shows whether each FAERS term was also recorded in these trials, with a real denominator (0 of 40 signal terms matched).
- NCT00510783 — IV Keppra in the Emergency Department for Prevention of Early Recurrent Seizures (N=158, PHASE4; 4 AE terms posted; arms: Phenytoin/Fosphenytoin; Levetiracetam)
Caveats: trial populations, doses and follow-up differ from the reporting population; AE terms are sponsor-coded and matched here by wording; absence from a trial list means the term was not reported above the sponsor's frequency threshold, not that it cannot occur.
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 |
|---|---|---|---|---|---|---|
| Drug ineffective (drug did not work) | 2,727 | 2.1 2.0–2.2ROR 2.3 · χ² 1,663 / p <1e-300 | 2.1 EB05 2.0 · IC025 +1.0 3/3 methods agree | Reporting / coding artifact | serious PRR 3.4 | not reported in cached trials |
| Drug interaction | 1,572 | 10.1 9.6–10.6ROR 10.9 · χ² 12,856 / p <1e-300 | 10.0 EB05 9.6 · IC025 +3.2 3/3 methods agree | Reporting / coding artifact | serious PRR 6.9 · 91% clinician | not reported in cached trials |
| Seizure | 1,415 | 12.6 12.0–13.3ROR 13.5 · χ² 15,003 / p <1e-300 | 12.5 EB05 11.9 · IC025 +3.5 3/3 methods agree | Likely indication confounding term in indications; also in warnings | serious PRR 8.2 | not reported in cached trials |
| Toxicity to various agents | 1,371 | 8.3 7.9–8.8ROR 8.8 · χ² 8,817 / p <1e-300 | 8.2 EB05 7.9 · IC025 +3.0 3/3 methods agree | Not in label — unassessed | serious PRR 5.4 · 95% clinician | not reported in cached trials |
| Convulsion (seizure) | 1,263 | 22.5 21.3–23.7ROR 23.9 · χ² 25,404 / p <1e-300 | 22.0 EB05 21.0 · IC025 +4.4 3/3 methods agree | Labeled (related wording) related wording | serious PRR 14.0 | not reported in cached trials |
| Off label use (used outside approved label) | 1,121 | 1.3 1.2–1.4ROR 1.3 · χ² 83 / p 3e-20 | 1.3 EB05 1.2 · IC025 +0.3 | Reporting / coding artifact | serious PRR 1.4 | not reported in cached trials |
| Status epilepticus | 804 | 77.3 72.0–82.9ROR 80.4 · χ² 56,154 / p <1e-300 | 71.7 EB05 67.6 · IC025 +6.0 3/3 methods agree | Labeled adverse reaction exact term | serious PRR 46.2 · 92% clinician | not reported in cached trials |
| Stevens-johnson syndrome (severe blistering skin reaction) | 771 | 36.2 33.7–38.9ROR 37.6 · χ² 25,464 / p <1e-300 | 34.9 EB05 32.9 · IC025 +5.0 3/3 methods agree | Labeled adverse reaction exact term | serious PRR 22.5 · 91% clinician | not reported in cached trials |
| Pyrexia (fever) | 685 | 2.0 1.9–2.2ROR 2.0 · χ² 348 / p 7e-78 | 2.0 EB05 1.9 · IC025 +0.9 | Labeled (related wording) related wording | serious PRR 1.6 | not reported in cached trials |
| Fall | 618 | 1.9 1.7–2.0ROR 1.9 · χ² 258 / p 3e-58 | 1.9 EB05 1.8 · IC025 +0.8 | Not in label — unassessed | serious PRR 1.4 | not reported in cached trials |
| Dizziness | 606 | 1.2 1.1–1.3ROR 1.2 · χ² 27 / p 1e-7 | 1.2 EB05 1.2 · IC025 +0.2 | Labeled adverse reaction exact term | serious PRR 1.2 | NCT00510783: 17/82 (20.7%) on Phenytoin |
| Drug reaction with eosinophilia and systemic symptoms | 603 | 24.4 22.5–26.4ROR 25.1 · χ² 13,209 / p <1e-300 | 23.8 EB05 22.3 · IC025 +4.4 3/3 methods agree | Labeled adverse reaction exact term | serious PRR 15.2 · 99% clinician | not reported in cached trials |
| Condition aggravated | 573 | 1.9 1.8–2.1ROR 1.9 · χ² 255 / p 1e-57 | 1.9 EB05 1.8 · IC025 +0.8 | Reporting / coding artifact | serious PRR 1.8 | not reported in cached trials |
| Somnolence (drowsiness) | 550 | 2.8 2.6–3.0ROR 2.8 · χ² 625 / p 4e-138 | 2.8 EB05 2.6 · IC025 +1.3 3/3 methods agree | Labeled adverse reaction exact term | serious PRR 2.9 | not reported in cached trials |
| Epilepsy | 532 | 17.9 16.5–19.5ROR 18.4 · χ² 8,344 / p <1e-300 | 17.6 EB05 16.4 · IC025 +4.0 3/3 methods agree | Labeled adverse reaction exact term | serious PRR 11.2 | not reported in cached trials |
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.
- Purple glove syndrome — n=65, PRR 981.4
- Inspiratory capacity decreased — n=97, PRR 552.3
- New onset refractory status epilepticus — n=31, PRR 417.4
- Postictal paralysis — n=35, PRR 171.0
- Necrosis ischaemic — n=54, PRR 133.5
- Intensive care unit acquired weakness — n=36, PRR 105.2
- Pneumatosis — n=33, PRR 81.0
- Sudden unexplained death in epilepsy — n=34, PRR 67.8
- Kidney malformation — n=21, PRR 63.0
- Propofol infusion syndrome — n=41, PRR 62.3
✓ A hand-written Bradford Hill causality assessment exists for this drug: Phenytoin ↔ Stevens–Johnson syndrome / TEN.
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 Phenytoin?
In FDA FAERS, the most frequently co-reported reaction terms for Phenytoin are seizure, toxicity to various agents, convulsion, status epilepticus, stevens-johnson syndrome, pyrexia. 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 Phenytoin have an FDA boxed warning?
No. The FDA label retrieved for Phenytoin has no boxed warning; see the label's Warnings and Precautions for the recognised risks.
Do FAERS signals prove that Phenytoin 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 08a9d26b-4419-43ec-98f3-43d4534c2e76, effective 20260429; matched on
openfda.generic_name.exact:"PHENYTOIN") - 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, 1,154 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 - ClinicalTrials.gov API v2 (query
PHENYTOIN, results-bearing studies sorted by enrollment)
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.