Prescription medication · Anticonvulsant (Hydantoin)
phenytoin
Also sold as Dilantin. This medicine treats generalized tonic-clonic status epilepticus, a type of prolonged seizure.
Data updated 2026-05-15
- 20,453
- FDA reportsModerately reported
- 147
- InteractionsMany interactions
- $1.61
- Generic price (NADAC)
What the data shows
phenytoin (Dilantin) is a prescription Anticonvulsant (Hydantoin), reported at a middle-of-the-pack volume (20,453 FDA reports), with 147 documented drug interactions.
Reporting volume reflects how widely a drug is used and studied, not how dangerous it is, a FAERS report documents a temporal association, never proof of cause.
phenytoin (Dilantin) is a prescription Anticonvulsant (Hydantoin). This medicine treats generalized tonic-clonic status epilepticus, a type of prolonged seizure.
Phenytoin injection is used to treat certain types of seizures. It can also prevent seizures during or after neurosurgery.
Verify with FDA → · CMS NADAC pricing →
Drug Pricing (NADAC)
Generic Price
$1.61/unit
Generic Available
Yes (13 manufacturers)
Pricing data from NADAC (CMS), effective December 18, 2024. Compare all drug costs →
What it does
This medicine treats generalized tonic-clonic status epilepticus, a type of prolonged seizure.
Common side effects
No common side effects listed.
Key warnings
This medicine can cause serious heart problems if given too quickly.
The sections below are summarized in plain English from phenytoin's FDA-approved prescribing information. They describe what the official label says, and are not personal medical advice.
How It Works
Phenytoin works by slowing down the signals in the brain that cause seizures. It stabilizes nerve cell membranes, reducing excessive electrical activity. This helps to prevent seizures from starting or spreading.
Side Effects (from patient reports)
Based on 20,453 FDA adverse event reports.
Most-reported reactions
Adverse reactions in FAERS for phenytoin, by number of reports
- Drug Interaction
Drug Interaction
1,547 reports
- Seizure
Seizure
1,382 reports
- Toxicity To Various Agents
Toxicity To Various Agents
1,353 reports
- Convulsion
Convulsion
1,262 reports
- Status Epilepticus
Status Epilepticus
791 reports
- Stevens-Johnson Syndrome
Stevens-Johnson Syndrome
770 reports
- Pyrexia
Pyrexia
683 reports
- Fall 609
Fall
609 reports
- Drug Reaction With Eosinophilia And Systemic Symptoms 600
Drug Reaction With Eosinophilia And Systemic Symptoms
600 reports
- Dizziness 597
Dizziness
597 reports
What this shows Bars show how often each reaction was reported, not how likely it is to happen, a report records a temporal association, never proof that the drug caused it.
Reports over time
Adverse-event reports filed for phenytoin each year to the FDA Adverse Event Reporting System (FAERS).
Year-to-year volume tracks usage, prescribing, and scrutiny, not a change in per-patient risk. Source: FDA FAERS.
Where phenytoin sits
phenytoin has more FDA adverse-event reports than 55% of the drugs FAERS tracks. A high position reflects how widely a drug is used and watched, not how dangerous it is.
Percentile across all drugs PlainMeds tracks by FAERS report volume. The dot is phenytoin; the line is the median (50th percentile).
FDA Adverse Event Report Analysis
Detailed analysis of 20,453 reports from the FDA Adverse Event Reporting System (FAERS). Reports span 2004–2025.
Total Reports
20,453
Reports Mentioning Death
2,949
14.4% of reports — not proof of cause
Hospitalization Reports
8,381
Top Indication
Product Used For Unknown Indication
Gender Distribution
Age Distribution
Most Reported Adverse Reactions (FAERS)
| # | Reaction | Reports |
|---|---|---|
| 2 | DRUG INTERACTION | 1,547 |
| 3 | SEIZURE | 1,382 |
| 4 | TOXICITY TO VARIOUS AGENTS | 1,353 |
| 5 | CONVULSION | 1,262 |
| 7 | STATUS EPILEPTICUS | 791 |
| 8 | STEVENS-JOHNSON SYNDROME | 770 |
| 9 | PYREXIA | 683 |
| 10 | FALL | 609 |
| 11 | DRUG REACTION WITH EOSINOPHILIA AND SYSTEMIC SYMPTOMS | 600 |
| 12 | DIZZINESS | 597 |
| 13 | CONDITION AGGRAVATED | 556 |
| 14 | SOMNOLENCE | 537 |
| 15 | EPILEPSY | 525 |
| 16 | CONFUSIONAL STATE | 520 |
| 17 | VOMITING | 520 |
Reactions in Death Reports
Reactions in Hospitalization Reports
Source: FDA FAERS (Adverse Event Reporting System) Reports are voluntary and do not establish causation
Serious Warnings
This medicine can cause serious heart problems if given too quickly. The injection rate should not be faster than 50 mg per minute for adults, and 1 to 3 mg/kg/min (or 50 mg per minute, whichever is slower) for children. Your heart will be monitored closely during and after the injection.
Known Drug Interactions
Anticonvulsants carbamazepine , phenobarbital, primidone, phenytoin ↓ nirmatrelvir/ritonavir Co-administration contraindicated due to potential loss of virologic response and possible resistance [see Contraindications (4) ] .
Mechanism: Phenytoin makes the body get rid of the antiviral medicine too quickly. This prevents the drug from working properly and could allow the virus to become harder to treat.
Interaction Drug Interaction Rifabutin, phenytoin, efavirenz, cimetidine, esomeprazole* Avoid coadministration unless the benefit outweighs the risks ( 7.6 , 7.7 , 7.8 , 7.9 ) Other drugs metabolized by CYP3A4 Consider dosage adjustment and monitor for adverse effects and toxicity ( 7.1 , 7.10 , 7.11 ) Digoxin Monitor digoxin plasma concentrations ( 7.12 ) Fosamprenavir, metoclopramide* Monitor for breakthrough fungal infections ( 7.6 , 7.13 ) *The drug interactions with esomeprazole and metoclopramide do not apply to posaconazole tablets. 7.8 Phenytoin Phenytoin induces UDP-glucuronidase...
Mechanism: Phenytoin causes the body to break down posaconazole much faster than usual, which can make the antifungal medicine less effective.
CYP3A Inducers Do not use ranolazine with CYP3A inducers such as rifampin, rifabutin, rifapentine, phenobarbital, phenytoin, carbamazepine, and St.
Mechanism: Phenytoin makes your body clear ranolazine much faster than it should, which lowers the drug's effectiveness.
Carbamazepine (CYP450 Induction) Not Studied In Vivo or In Vitro , but Likely to Result in Significant Reduction Contraindicated Long Acting Barbiturates (e.g., phenobarbital, mephobarbital) (CYP450 Induction) Not Studied In Vivo or In Vitro , but Likely to Result in Significant Reduction Contraindicated Phenytoin (CYP450 Induction) Significantly Reduced Increase voriconazole maintenance dose from 4 mg/kg to 5 mg/kg IV every 12 hours or from 200 mg to 400 mg orally every 12 hours (100 mg to 200 mg orally every 12 hours in patients weighing less than 40 kg). Phenytoin (CYP2C9 Inhibition)...
Mechanism: Phenytoin speeds up how fast the body gets rid of voriconazole, while voriconazole slows down the breakdown of phenytoin. This means the antifungal may not work well, and the seizure medicine could reach toxic levels.
7.2 Combined P-gp Strong CYP3A4 Inducers Avoid concomitant use of apixaban tablets with combined P-gp and strong CYP3A4 Inducers (e.g., rifampin, carbamazepine, phenytoin, St.
Mechanism: Phenytoin causes your body to get rid of apixaban much faster than it should. This means the medicine may not work well enough to stop blood clots from forming.
This is a plain-language summary of FDA-label interaction records and does not provide individual medication-combination directions.
Common Questions
What should I tell my doctor before taking phenytoin?
Can I take phenytoin with other medicines?
What are the signs of an allergic reaction to phenytoin?
Will phenytoin cure my seizures?
Can I drink alcohol while taking phenytoin?
What happens if I stop taking phenytoin suddenly?
Does phenytoin affect birth control?
Can phenytoin cause gum overgrowth?
Will phenytoin affect my ability to drive or operate machinery?
How often will I need blood tests while taking phenytoin?
Does phenytoin interact with other medications?
What drug class is phenytoin?
What pregnancy or breastfeeding source fields are listed for phenytoin?
Related Medications in Anticonvulsant (Hydantoin)
Other drugs grouped near phenytoin - same-class peers and common alternatives.
brivaracetam
Briviact
Brivaracetam is a medicine used to treat partial-onset seizures.
Compare with phenytoin →
cannabidiol
Epidiolex
Epidiolex is a medicine that contains cannabidiol.
Compare with phenytoin →
carbamazepine
Tegretol
Carbamazepine is a medicine used to control seizures and treat nerve pain.
Compare with phenytoin →
cenobamate
Xcopri
Xcopri is a medicine used to treat partial-onset seizures in adults.
Compare with phenytoin →
clobazam
Onfi, Sympazan
Clobazam oral suspension is a medicine used with other medicines to treat seizures caused by Lennox-Gastaut syndrome.
Compare with phenytoin →
Compare beyond drug class
Nationwide peers by FAERS volume & death-report share
Two PlainMeds-derived comparison paths for phenytoin: nearest FDA FAERS report volume and nearest death-report share among drugs with at least 1,000 logged reports, excluding same-class neighbors listed above. Counts reflect reporting volume, not proven individual harm.
Similar FAERS report volume
Nearest drugs by total FAERS reports. This record: 20,453.
Similar death-report share
Nearest drugs by FAERS death-report share. This record: 14.42%.
- hydroxyzine Δ 0.05 pts · 44,206 reports · Antihistamine / Anxiolytic 14.37%death share
- cyclobenzaprine Δ 0.05 pts · 47,426 reports · Muscle Relaxant 14.47%death share
- lorazepam Δ 0.08 pts · 174,469 reports · Benzodiazepine 14.34%death share
- fluvastatin Δ 0.10 pts · 3,948 reports · HMG-CoA Reductase Inhibitor (Statin) 14.51%death share
Medication Guides
Understanding Drug Interactions
How CYP450 enzymes, inhibitors, and inducers affect your medications
Generic vs Brand Name Drugs
FDA requirements, cost savings, and when the difference matters
Narrow Therapeutic Index Drugs
FDA bioequivalence and label-record context for narrow therapeutic index medicines
Common Drug Interactions
Dangerous medication combinations and how to protect yourself
Save on phenytoin
Compare prices and find discounts at pharmacies near you. Free coupons can save up to 80% on prescriptions.
Disclosure: This link may earn us a commission at no extra cost to you. See our terms.
What the FDA Data Shows for phenytoin
The FDA label for phenytoin (sold under brand names such as Dilantin) classifies it as a prescription-only medication in the Anticonvulsant (Hydantoin) class. This medicine treats generalized tonic-clonic status epilepticus, a type of prolonged seizure. Labeling covers dosing, contraindications, and monitoring requirements derived from clinical trials.
Post-market surveillance from the FDA Adverse Event Reporting System (FAERS) captures real-world experience. For this drug, FAERS contains 20,453 voluntary reports. The database also lists 147 documented drug interactions derived from FDA labeling, with the top-flagged interaction rated major severity. NADAC pricing from CMS shows a generic unit cost of $1.61.
Report counts do not establish causation, a FAERS entry documents a temporal association, not proof that the drug produced the outcome. Widely prescribed medications naturally accumulate more reports than niche therapies, so raw totals must be interpreted alongside total exposure. Shortage status, recall history, and patent information are separate source-record fields. This page is a public FDA/CMS registry and does not provide medical, treatment, substitution, or medication-change directions.
Data Sources
Drug labeling: FDA Drug Labels (SPL/DailyMed). Adverse events: FDA Adverse Event Reporting System (FAERS). Pricing: CMS National Average Drug Acquisition Cost (NADAC).
FAERS reports are voluntary and do not establish causation. Drug interactions are derived from FDA labeling and clinical references. This registry does not provide medication decisions.
Last updated: April 9, 2024
PlainMeds is rendered directly from FDA openFDA/FAERS extracts, DailyMed labels, and CMS drug-pricing files, no number is typed in by an editor. FAERS counts, recalls, shortages, and price figures on this page are queried live from those federal extracts. See our editorial standards & corrections policy, the methodology behind these numbers, or report a data error. Data current as of 2026-05-15. Primary sources: openFDA / FAERS, DailyMed and CMS Part B ASP.
Read our methodology - how this data is sourced, computed, and verified.
Data currency: FDA FAERS adverse-event reports through 2025, CMS NADAC acquisition-cost pricing effective December 2024, compiled from the source snapshot dated . See our methodology for per-source dates and refresh cadence. Spot a figure that looks wrong? Report a data issue.
All federal data sources used on this page
- FDA Orange Book - approved drug products with therapeutic equivalence. accessdata.fda.gov/cder/ob
- FDA DailyMed - NIH-hosted drug labeling for FDA-approved meds. dailymed.nlm.nih.gov
- FDA Adverse Event Reporting System (FAERS) - post-marketing safety surveillance. fda.gov/drugs/faers
- NLM RxNorm - standardized clinical drug nomenclature. nlm.nih.gov/research/umls/rxnorm
- CMS Medicare Part B Drug Average Sales Price Files - federal drug pricing data. cms.gov/medicare/part-b-drugs/asp
- FDA Drug Shortages Database - current and resolved drug shortage tracking. accessdata.fda.gov/drugshortages