Last reviewed 2026-04-19 · How we verify

Dilantin (Phenytoin Sodium)

Phenytoin exerts its therapeutic effect by voltage-dependent blockade of membrane sodium channels.

Dilantin is an anti-seizure medication by Pfizer Inc. It works by blocking sodium channels in the brain. It's used to prevent tonic-clonic and focal seizures, but not absence seizures. The intravenous form is used for status epilepticus and certain heart arrhythmias. It can be taken intravenously or orally. Dilantin is a significant commercial product with $63.6B revenue and 414 publications.

At a glance

Mechanism of action

The precise mechanism of action of phenytoin is not fully understood, but it's thought to involve the blockade of sodium channels in the brain. This blockade reduces sustained high-frequency neuronal discharges, which are associated with seizures. By reducing these discharges, phenytoin helps to prevent seizures.

Approved indications

• Bipolar disorder in remission
• Epilepsy
• Epilepsy characterized by intractable complex partial seizures
• Lennox-Gastaut syndrome
• Localization-related epilepsy
• Motor cortex epilepsy
• Prevention of Seizures following Cranial Trauma or Surgery
• Seizures in Neurosurgery
• Simple partial seizure
• Status epilepticus
• Tonic-clonic epilepsy
• Tonic-clonic seizure

Boxed warnings

• WARNING: CARDIOVASCULAR RISK ASSOCIATED WITH RAPID INFUSION The rate of intravenous Phenytoin Sodium Injection administration should not exceed 50 mg per minute in adults and 1 to 3 mg/kg/min (or 50 mg per minute, whichever is slower) in pediatric patients because of the risk of severe hypotension and cardiac arrhythmias. Careful cardiac monitoring is needed during and after administering intravenous Phenytoin Sodium Injection. Although the risk of cardiovascular toxicity increases with infusion rates above the recommended infusion rate, these events have also been reported at or below the recommended infusion rate. Reduction in rate of administration or discontinuation of dosing may be needed [see Dosage and Administration (2.1) and Warnings and Precautions (5.1) ] . W ARN ING: CARDIOVASCULAR RISK ASSOCIATED WITH RAPID INFUSION S ee full prescribing information for complete boxed warning . The rate of intravenous Phenytoin Sodium Injection administration should not exceed 50 mg per minute in adults and 1 to 3 mg/kg/min (or 50 mg per minute, whichever is slower) in pediatric patients because of the risk of severe hypotension and cardiac arrhythmias. Careful cardiac monitoring is needed during and after administering intravenous Phenytoin Sodium Injection. Reduction in rate of administration or discontinuation of dosing may be needed ( 2.1 , 5.1 ).

Common side effects

• Withdrawal Precipitated Seizure, Status Epilepticus
• Suicidal Behavior and Ideation
• Serious Dermatologic Reactions
• Drug Reaction with Eosinophilia and Systemic Symptoms (DRESS)/Multiorgan Hypersensitivity
• Hypersensitivity
• Cardiac Effects
• Angioedema
• Hepatic Injury
• Hematopoietic Complications
• Effects on Vitamin D and Bone
• Exacerbation of Porphyria
• Teratogenicity and Other Harm to the Newborn

Drug interactions

• CYP2B6 Substrates
• CYP2C19 Substrates
• CYP2C8 Substrates
• CYP2C9 Substrates
• CYP3A4 Substrates
• P-glycoprotein Substrates
• aripiprazole
• fluorouracil
• metyrapone
• mexiletine
• quetiapine
• quinestrol

Key clinical trials

• A Study to Evaluate VH4524184 Tablet Absorption, Effects of Food, and Interactions With Other Drugs in Healthy Adults (PHASE1)
• A Study of the Effect of Itraconazole and Phenytoin on Calderasib (MK-1084) in Healthy Adults (MK-1084-008) (PHASE1)
• Levetiracetam Versus Phenobarbitone for the Treatment of Neonatal Seizures in a Tertiary Care Hospital. (NA)
• Effect of Phenytoin or Itraconazole on How BGB-16673 is Absorbed and Removed From the Body in Healthy Participants (PHASE1)
• Population Pharmacokinetics of Antiepileptic in Pediatrics
• Antiseizure Medication in Seizure Networks at Early Acute Brain Injury (PHASE4)
• Drug-Drug Interaction Study of Casdatifan in Healthy Adult Participants (ARC-29) (PHASE1)
• Early Post-Traumatic Seizures Prevention Trial (E-PTS Trial) (PHASE4)

Primary sources

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