Drug · FAERS side-effect profile with label screen
Extended Phenytoin side effects: what 16,631 FDA adverse event reports show
Drug class
Not stated in label
Label matched
Extended Phenytoin Sodium (Phenytek)
closest FDA label found for this product string; brand list suppressed because the label is a related product, not an exact match
Who reports
16,631 reports · 72% serious · 1,202 with death outcome · 56% female
openFDA FAERS counts, all years, deduplication not applied
Used for
PHENYTEK ® capsules (extended phenytoin sodium capsules) are indicated for the treatment of tonic-clonic (grand mal) and psychomotor (temporal lobe) seizures and prevention and treatment of seizures occurring during or following neurosurgery. PHENYTEK .
FDA label, Indications and Usage
What it is
Phenytoin sodium 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 3Labeled (related wording) 6Likely indication confounding 7Reporting / coding artifact 6Lab value / disease marker 5Not in label — unassessed 13
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. 1,108 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 |
|---|---|---|---|---|---|---|
| Anticonvulsant toxicity | 19 | 761.8 430.5–1,348.3ROR 762.7 · χ² 8,485 / p <1e-300 | 320.2 EB05 216.7 · IC025 +4.4 3/3 methods agree | Labeled (related wording) related wording | serious n=19 | no trial arm names this drug |
| Anticonvulsant drug level abnormal | 61 | 665.1 487.6–907.3ROR 667.6 · χ² 25,919 / p <1e-300 | 381.6 EB05 307.8 · IC025 +6.2 3/3 methods agree | Lab value / disease marker | serious n=47 | no trial arm names this drug |
| Anticonvulsant drug level decreased | 370 | 442.6 393.5–497.9ROR 452.7 · χ² 119,909 / p <1e-300 | 321.2 EB05 294.7 · IC025 +7.7 3/3 methods agree | Lab value / disease marker | serious n=334 | no trial arm names this drug |
| Anticonvulsant drug level below therapeutic | 163 | 344.0 289.4–408.9ROR 347.4 · χ² 43,395 / p <1e-300 | 261.4 EB05 229.4 · IC025 +7.0 3/3 methods agree | Lab value / disease marker | serious n=146 | no trial arm names this drug |
| Anticonvulsant drug level increased | 315 | 303.3 268.4–342.7ROR 309.1 · χ² 76,055 / p <1e-300 | 240.4 EB05 219.0 · IC025 +7.3 3/3 methods agree | Lab value / disease marker | serious n=261 | no trial arm names this drug |
| Cerebellar atrophy | 124 | 205.8 170.3–248.7ROR 207.3 · χ² 21,506 / p <1e-300 | 172.0 EB05 148.1 · IC025 +6.4 3/3 methods agree | Labeled adverse reaction exact term | serious n=124 | no trial arm names this drug |
| Anticonvulsant drug level above therapeutic | 73 | 158.9 124.6–202.7ROR 159.6 · χ² 10,017 / p <1e-300 | 136.1 EB05 111.8 · IC025 +5.8 3/3 methods agree | Lab value / disease marker | serious n=63 | no trial arm names this drug |
| Drug level fluctuating | 69 | 107.3 84.0–137.2ROR 107.8 · χ² 6,594 / p <1e-300 | 96.3 EB05 78.7 · IC025 +5.5 3/3 methods agree | Reporting / coding artifact | serious n=48 | no trial arm names this drug |
| Drug level changed | 47 | 100.7 74.9–135.5ROR 101.0 · χ² 4,201 / p <1e-300 | 89.9 EB05 70.4 · IC025 +5.1 3/3 methods agree | Reporting / coding artifact | serious n=30 | no trial arm names this drug |
| Epileptic aura | 16 | 83.2 50.2–138.0ROR 83.3 · χ² 1,142 / p 1e-250 | 71.6 EB05 46.8 · IC025 +3.7 3/3 methods agree | Not in label — unassessed | serious n=14 | no trial arm names this drug |
| Gingival hyperplasia | 33 | 72.3 50.9–102.7ROR 72.5 · χ² 2,127 / p <1e-300 | 65.9 EB05 49.1 · IC025 +4.5 3/3 methods agree | Labeled adverse reaction exact term | serious n=26 | no trial arm names this drug |
| Aura | 88 | 62.6 50.5–77.5ROR 62.9 · χ² 5,019 / p <1e-300 | 58.9 EB05 49.3 · IC025 +5.1 3/3 methods agree | Not in label — unassessed | serious n=71 · 72% consumer | no trial arm names this drug |
| Complex partial seizures | 48 | 56.0 42.0–74.8ROR 56.2 · χ² 2,430 / p <1e-300 | 52.6 EB05 41.2 · IC025 +4.6 3/3 methods agree | Likely indication confounding shares a disease stem with the indications wording | serious n=45 | no trial arm names this drug |
| Vagal nerve stimulator implantation | 12 | 53.1 29.8–94.6ROR 53.1 · χ² 539 / p 1e-119 | 47.4 EB05 28.9 · IC025 +3.1 3/3 methods agree | Not in label — unassessed | serious n=11 | no trial arm names this drug |
| Convulsion (seizure) | 2,170 | 49.0 47.1–51.0ROR 56.2 · χ² 98,351 / p <1e-300 | 47.1 EB05 45.5 · IC025 +5.5 3/3 methods agree | Labeled (related wording) related wording | serious PRR 37.6 | no trial arm names this drug |
| Simple partial seizures | 29 | 46.4 32.0–67.2ROR 46.5 · χ² 1,198 / p 7e-263 | 43.6 EB05 31.8 · IC025 +4.1 3/3 methods agree | Likely indication confounding shares a disease stem with the indications wording | serious n=28 | no trial arm names this drug |
| Encephalomalacia | 20 | 46.0 29.5–71.9ROR 46.1 · χ² 807 / p 9e-178 | 42.8 EB05 29.2 · IC025 +3.7 3/3 methods agree | Not in label — unassessed | serious n=20 · ♀ 30% (drug 56%) | no trial arm names this drug |
| Grand mal convulsion | 328 | 45.7 41.0–51.0ROR 46.6 · χ² 13,804 / p <1e-300 | 44.0 EB05 40.2 · IC025 +5.2 3/3 methods agree | Not in label — unassessed | serious PRR 35.1 | no trial arm names this drug |
| Focal dyscognitive seizures | 32 | 36.3 25.5–51.6ROR 36.4 · χ² 1,033 / p 6e-227 | 34.6 EB05 25.7 · IC025 +3.9 3/3 methods agree | Likely indication confounding shares a disease stem with the indications wording | serious n=31 | no trial arm names this drug |
| Glioblastoma multiforme | 23 | 35.1 23.2–53.1ROR 35.2 · χ² 709 / p 2e-156 | 33.3 EB05 23.4 · IC025 +3.6 3/3 methods agree | Not in label — unassessed | serious n=22 | no trial arm names this drug |
| Temporal lobe epilepsy | 11 | 32.2 17.7–58.7ROR 32.3 · χ² 295 / p 2e-66 | 30.0 EB05 17.8 · IC025 +2.7 3/3 methods agree | Likely indication confounding shares a disease stem with the indications wording | serious n=11 | no trial arm names this drug |
| Drug level decreased | 251 | 31.7 28.0–35.9ROR 32.2 · χ² 7,250 / p <1e-300 | 30.9 EB05 27.8 · IC025 +4.7 3/3 methods agree | Reporting / coding artifact | serious PRR 24.2 | no trial arm names this drug |
| Petit mal epilepsy | 107 | 27.1 22.4–32.8ROR 27.2 · χ² 2,605 / p <1e-300 | 26.4 EB05 22.5 · IC025 +4.2 3/3 methods agree | Not in label — unassessed | serious n=103 · 73% consumer | no trial arm names this drug |
| Stevens-johnson syndrome (severe blistering skin reaction) | 467 | 27.0 24.6–29.5ROR 27.7 · χ² 11,418 / p <1e-300 | 26.4 EB05 24.4 · IC025 +4.5 3/3 methods agree | Labeled adverse reaction exact term | serious PRR 21.4 | no trial arm names this drug |
| Transverse sinus thrombosis | 11 | 26.7 14.7–48.4ROR 26.7 · χ² 241 / p 1e-54 | 25.0 EB05 14.7 · IC025 +2.6 3/3 methods agree | Not in label — unassessed | serious n=11 | no trial arm names this drug |
| Therapeutic response unexpected with drug substitution | 84 | 25.6 20.7–31.8ROR 25.8 · χ² 1,924 / p <1e-300 | 25.0 EB05 20.8 · IC025 +4.1 3/3 methods agree | Reporting / coding artifact | serious n=66 | no trial arm names this drug |
| Cerebellar ataxia | 19 | 25.4 16.1–39.9ROR 25.4 · χ² 412 / p 6e-92 | 24.3 EB05 16.4 · IC025 +3.2 3/3 methods agree | Labeled (related wording) related wording | serious n=19 | no trial arm names this drug |
| Partial seizures | 100 | 24.9 20.4–30.3ROR 25.0 · χ² 2,227 / p <1e-300 | 24.3 EB05 20.6 · IC025 +4.1 3/3 methods agree | Likely indication confounding shares a disease stem with the indications wording | serious n=91 | no trial arm names this drug |
| Throat lesion | 12 | 22.5 12.7–39.8ROR 22.5 · χ² 221 / p 2e-50 | 21.2 EB05 12.6 · IC025 +2.6 3/3 methods agree | Not in label — unassessed | serious n=12 | no trial arm names this drug |
| Postictal state | 17 | 21.0 13.0–34.0ROR 21.1 · χ² 300 / p 2e-67 | 20.2 EB05 13.2 · IC025 +2.9 3/3 methods agree | Not in label — unassessed | serious n=17 | no trial arm names this drug |
| Brain operation | 37 | 21.0 15.2–29.1ROR 21.1 · χ² 674 / p 7e-149 | 20.5 EB05 15.5 · IC025 +3.5 3/3 methods agree | Reporting / coding artifact | serious n=37 · 75% consumer | no trial arm names this drug |
| Gingival disorder | 61 | 20.2 15.7–26.0ROR 20.3 · χ² 1,076 / p 2e-236 | 19.8 EB05 15.9 · IC025 +3.7 3/3 methods agree | Labeled (related wording) related wording | serious n=51 · 78% consumer | no trial arm names this drug |
| Intracranial venous sinus thrombosis | 17 | 20.0 12.4–32.4ROR 20.1 · χ² 284 / p 4e-64 | 19.2 EB05 12.5 · IC025 +2.9 3/3 methods agree | Not in label — unassessed | serious n=17 | no trial arm names this drug |
| Drug level below therapeutic | 86 | 20.0 16.2–24.8ROR 20.1 · χ² 1,511 / p <1e-300 | 19.6 EB05 16.4 · IC025 +3.8 3/3 methods agree | Reporting / coding artifact | serious n=67 | no trial arm names this drug |
| Generalised tonic-clonic seizure | 255 | 19.9 17.6–22.5ROR 20.2 · χ² 4,501 / p <1e-300 | 19.6 EB05 17.7 · IC025 +4.0 3/3 methods agree | Labeled (related wording) related wording | serious PRR 15.8 · 73% consumer | no trial arm names this drug |
| Gingival hypertrophy | 23 | 19.6 13.0–29.6ROR 19.6 · χ² 381 / p 3e-85 | 19.0 EB05 13.2 · IC025 +3.1 3/3 methods agree | Not in label — unassessed | serious n=20 | no trial arm names this drug |
| Apallic syndrome | 11 | 19.3 10.6–35.0ROR 19.3 · χ² 170 / p 3e-39 | 17.9 EB05 9.9 · IC025 +2.4 3/3 methods agree | Not in label — unassessed | serious n=11 | no trial arm names this drug |
| Atonic seizures | 12 | 19.2 10.9–34.0ROR 19.3 · χ² 187 / p 8e-43 | 18.0 EB05 10.3 · IC025 +2.5 3/3 methods agree | Likely indication confounding shares a disease stem with the indications wording | serious n=11 | no trial arm names this drug |
| Therapeutic agent toxicity | 47 | 17.8 13.3–23.7ROR 17.8 · χ² 716 / p 4e-158 | 17.4 EB05 13.6 · IC025 +3.4 3/3 methods agree | Labeled (related wording) related wording | serious n=47 | no trial arm names this drug |
| Seizure cluster | 11 | 17.5 9.6–31.7ROR 17.5 · χ² 153 / p 2e-35 | 16.0 EB05 8.6 · IC025 +2.3 3/3 methods agree | Likely indication confounding shares a disease stem with the indications wording | serious n=11 | no trial arm names this drug |
Trial evidence (ClinicalTrials.gov)
ClinicalTrials.gov returned results-bearing trials mentioning Extended Phenytoin only as a background or rescue medication (NCT01713946, NCT00774306); no trial listing it as the tested intervention was cached, so no trial cross-check is shown.
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 |
|---|---|---|---|---|---|---|
| Convulsion (seizure) | 2,170 | 49.0 47.1–51.0ROR 56.2 · χ² 98,351 / p <1e-300 | 47.1 EB05 45.5 · IC025 +5.5 3/3 methods agree | Labeled (related wording) related wording | serious PRR 37.6 | no trial arm names this drug |
| Seizure | 1,432 | 15.9 15.1–16.7ROR 17.3 · χ² 19,861 / p <1e-300 | 15.7 EB05 15.1 · IC025 +3.9 3/3 methods agree | Likely indication confounding term in indications; also in warnings | serious PRR 12.5 | no trial arm names this drug |
| Drug ineffective (drug did not work) | 1,280 | 1.2 1.2–1.3ROR 1.2 · χ² 56 / p 3e-14 | 1.2 EB05 1.2 · IC025 +0.2 | Reporting / coding artifact | serious PRR 1.7 · 70% consumer | no trial arm names this drug |
| Fall | 912 | 3.5 3.3–3.7ROR 3.6 · χ² 1,618 / p <1e-300 | 3.5 EB05 3.3 · IC025 +1.7 3/3 methods agree | Not in label — unassessed | serious PRR 3.0 | no trial arm names this drug |
| Drug hypersensitivity | 855 | 5.6 5.2–5.9ROR 5.8 · χ² 3,217 / p <1e-300 | 5.5 EB05 5.2 · IC025 +2.4 3/3 methods agree | Labeled (related wording) related wording | serious PRR 2.6 | no trial arm names this drug |
| Dizziness | 853 | 2.2 2.0–2.3ROR 2.2 · χ² 543 / p 2e-120 | 2.2 EB05 2.0 · IC025 +1.0 3/3 methods agree | Labeled adverse reaction exact term | serious PRR 2.3 | no trial arm names this drug |
| Headache | 832 | 1.7 1.6–1.8ROR 1.7 · χ² 233 / p 7e-53 | 1.7 EB05 1.6 · IC025 +0.6 | Labeled adverse reaction exact term | serious PRR 2.2 | no trial arm names this drug |
| Fatigue (tiredness) | 808 | 1.3 1.2–1.4ROR 1.3 · χ² 62 / p 2e-15 | 1.3 EB05 1.2 · IC025 +0.3 | Not in label — unassessed | serious PRR 1.5 | no trial arm names this drug |
| Nausea | 708 | 1.1 1.1–1.2ROR 1.1 · χ² 11 / p 4e-4 | 1.1 EB05 1.1 · IC025 +0.1 | Labeled adverse reaction exact term | serious PRR 1.3 | no trial arm names this drug |
| Pain | 582 | 1.2 1.1–1.3ROR 1.2 · χ² 18 / p 9e-6 | 1.2 EB05 1.1 · IC025 +0.1 | Not in label — unassessed | serious PRR 1.3 | no trial arm names this drug |
| Asthenia (weakness) | 571 | 1.9 1.8–2.1ROR 1.9 · χ² 253 / p 3e-57 | 1.9 EB05 1.8 · IC025 +0.8 | Not in label — unassessed | serious PRR 1.9 | no trial arm names this drug |
| Rash | 554 | 1.6 1.5–1.7ROR 1.6 · χ² 130 / p 2e-30 | 1.6 EB05 1.5 · IC025 +0.5 | Labeled adverse reaction exact term | serious PRR 1.8 | no trial arm names this drug |
| Vomiting | 538 | 1.4 1.3–1.6ROR 1.5 · χ² 75 / p 2e-18 | 1.4 EB05 1.3 · IC025 +0.4 | Labeled adverse reaction exact term | serious PRR 1.4 | no trial arm names this drug |
| Weight decreased (weight loss) | 511 | 2.3 2.1–2.5ROR 2.4 · χ² 383 / p 1e-85 | 2.3 EB05 2.1 · IC025 +1.1 3/3 methods agree | Not in label — unassessed | serious PRR 2.4 | no trial arm names this drug |
| Somnolence (drowsiness) | 486 | 3.1 2.8–3.3ROR 3.1 · χ² 673 / p 9e-149 | 3.0 EB05 2.8 · IC025 +1.5 3/3 methods agree | Labeled adverse reaction exact term | serious PRR 3.0 | no trial arm names this drug |
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.
- Aura — n=88, PRR 62.6
- Encephalomalacia — n=20, PRR 46.0
- Grand mal convulsion — n=328, PRR 45.7
- Glioblastoma multiforme — n=23, PRR 35.1
- Petit mal epilepsy — n=107, PRR 27.1
- Gingival hypertrophy — n=23, PRR 19.6
✓ 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 Extended Phenytoin?
In FDA FAERS, the most frequently co-reported reaction terms for Extended Phenytoin are convulsion, seizure, fall, drug hypersensitivity, dizziness, headache. 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 Extended Phenytoin have an FDA boxed warning?
No. The FDA label retrieved for Extended Phenytoin has no boxed warning; see the label's Warnings and Precautions for the recognised risks.
Do FAERS signals prove that Extended 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 0f94c791-8b07-4b41-927e-c9f28bec5f60, effective 20241015; matched on
openfda.generic_name.exact:"EXTENDED PHENYTOIN SODIUM") - 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, 1,148 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
EXTENDED 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.