Phenytoin XR: A Complete Overview

Phenytoin XR is an extended-release form of phenytoin sodium, a hydantoin anticonvulsant medication used to prevent and control seizures.

First approved by the FDA decades ago, Phenytoin XR remains one of the most widely prescribed seizure medications in the world. Whether you've just been prescribed it or you're looking for a clear explanation of what it does, this guide covers everything you need to know in 2026.

What Is Phenytoin XR?

Phenytoin XR is the extended-release capsule form of phenytoin sodium. "Extended-release" (sometimes labeled "XR" or "ER") means the medication is designed to dissolve slowly in your body, providing steady seizure protection throughout the day.

You may see Phenytoin XR sold under several names:

• Dilantin Kapseals — The original brand name
• Phenytek — Another brand name
• Generic phenytoin sodium extended-release — Available from multiple manufacturers

Phenytoin belongs to a class of drugs called hydantoin anticonvulsants. It works by blocking voltage-dependent sodium channels in the brain, which stops the rapid, repetitive nerve firing that causes seizures.

What Is Phenytoin XR Used For?

Phenytoin XR is FDA-approved for:

• Generalized tonic-clonic (grand mal) seizures — The most common type of epileptic seizure, involving loss of consciousness and convulsions.
• Complex partial seizures — Seizures that affect awareness, often starting in one area of the brain.
• Seizure prevention during or after neurosurgery — Used to prevent seizures in patients who have had brain surgery.

Doctors sometimes prescribe Phenytoin XR off-label for conditions like trigeminal neuralgia (a type of facial nerve pain) and other neuropathic pain conditions.

How Is Phenytoin XR Taken?

Phenytoin XR comes as extended-release capsules in three strengths: 100 mg, 200 mg, and 300 mg.

Important dosing information:

• Typical dose range — Most adults take 200 mg to 600 mg daily, with 300 mg to 400 mg being the most common dose.
• Once or twice daily — The extended-release form can often be taken once a day, though some patients take it in divided doses.
• Swallow whole — Do not crush, chew, or open the capsules. This would destroy the extended-release mechanism and cause the drug to release too quickly.
• With or without food — You can take Phenytoin XR with or without food, but taking it consistently the same way each day helps maintain steady blood levels.
• Blood level monitoring — Because Phenytoin XR has a narrow therapeutic index, your doctor will order regular blood tests. The target blood level is typically 10–20 mcg/mL.

Important: Do not switch between brand-name and generic Phenytoin XR — or between different generic manufacturers — without your doctor's guidance. Small differences in how the drug is absorbed can affect your seizure control.

Who Should Not Take Phenytoin XR?

Phenytoin XR is not right for everyone. You should not take it if you:

• Are allergic to phenytoin or other hydantoin medications
• Are taking delavirdine (an HIV medication) — this combination is contraindicated
• Are pregnant or planning to become pregnant — Phenytoin XR is Pregnancy Category D and can cause birth defects (fetal hydantoin syndrome)

Your doctor should also use caution if you:

• Have liver disease
• Have low albumin levels or kidney problems (these affect drug levels)
• Are of Southeast Asian descent (higher risk of serious skin reactions — genetic testing for HLA-B*1502 is recommended)
• Are elderly (may need lower doses)

Always tell your doctor about all medications and supplements you take, as Phenytoin XR has many drug interactions.

How Much Does Phenytoin XR Cost?

The cost of Phenytoin XR depends on whether you're getting the brand name or generic, and whether you have insurance:

• Generic with insurance — Most patients pay a low copay (often $0–$15) since generic phenytoin ER is typically on the lowest formulary tier.
• Generic without insurance — Cash price ranges from about $18 to $120 for a 30-day supply depending on dose and pharmacy.
• With a discount coupon — Sites like GoodRx, SingleCare, and others can bring the cost to $18–$45 for a 90-count supply of 100 mg capsules.
• Brand-name Dilantin — Significantly more expensive and may require prior authorization from insurance.

For a complete breakdown of savings options, see our guide on how to save money on Phenytoin XR.

Final Thoughts

Phenytoin XR is a proven, effective seizure medication with a long track record. It requires more monitoring than some newer anticonvulsants, but for many patients, it provides reliable seizure control at an affordable price.

If you're having trouble finding Phenytoin XR at your pharmacy, Medfinder can help you locate it in stock near you. And if you have questions about side effects or alternatives, we've got guides for those too.