COMMON BRAND: Dilantin, Di-Phen, Euthasol, Phenytek

Phenytoin is an oral prescription drug, belongs to a class of drugs known as antiepileptic or anticonvulsant drugs. This antiepileptic drugs (AEDs) works by blocking the spread of seizure activity in the brain. Phenytoin oral capsule is available as the brand-name drugs and generic name drug. Generic drugs usually cost less.

What is Phenytoin used for?

Phenytoin is used to treat tonic-clonic and complex partial seizures (but not absence seizures) in people with epilepsy. This drug works by reducing the spread of seizure activity in the brain occurring during or after neurosurgery.

How to use Phenytoin?

Read patient information leaflet carefully and follow all the instructions. Take phenytoin exactly as prescribed. Avoid taking more or less of it or take it more frequently than instructed by your doctor.

The body absorbs the different form of phenytoin in different ways and can’t be substituted for one another. If you require to switch from one phenytoin form to other, your doctor may need to adjust your dose. Every time you get a refill, make sure that you have received the phenytoin form that was prescribed to you.

The dose of your drug is based on your medical condition and response to treatment. Make sure to take medication at the same time each day to avoid confusion or to miss a dose. Take this medicine regularly to get the full benefit from it.

If you are taking antacids and nutritional tube-feeding products that may hinder the absorption of phenytoin. Avoid taking these products at the same time with phenytoin.

Do not stop using phenytoin without consulting your doctor, even if you feel better or experience side effects like unusual changes in behavior or mood. If you discontinue taking phenytoin, your seizures may get worse. Your dose needs to be decreased gradually.

What are the side effects of Phenytoin?

Common side effects that can occur with this drug such as slurred speech, confusion, dizziness, trouble sleeping, problems with walking and coordination, nervousness, tremors, headache, nausea or vomiting, constipation, skin rash. If any of these effects remain or worsen, inform to your doctor or pharmacist immediately.

Get medical assistance immediately if you notice any of these severe side effects such as loss of coordination, unusual eye movements, double or blurred vision, slurred speech, confusion, muscle twitching, tingling of the hands/feet, facial changes (like swollen lips, butterfly-shaped rash around the nose/cheeks), increased thirst or urination, excessive hair growth, unusual tiredness, bone or joint pain, easily broken bones.

This drug may cause swelling and bleeding of the gums. Brushing and flossing your teeth and see a dentist regularly can help to prevent this from happening.

A severe allergic reaction to this drug is very rare. Get medical assistance right away if you notice any of these symptoms such as fever, rash, swollen lymph nodes, itching/swelling (especially of the face/tongue/throat), severe dizziness, trouble breathing.

Some people who take phenytoin may experience depression, suicidal thoughts/attempts, or other mental/mood problems. Inform your doctor right away if you or your family member notice any unusual changes in your mood, thoughts, or behavior.

Phenytoin may increase your blood sugar level. Discuss with your doctor if you have diabetes.

Get emergency medical assistance right away if you observe signs of liver problems (like nausea/vomiting that doesn’t stop, stomach/abdominal pain, yellowing eyes/skin, dark urine).

This is not a full record of all possible side effects. If you mark other effects not listed above, contact your doctor or pharmacist.

What are the precautions while using Phenytoin?

Inform to your doctor if you are allergic to it or other anticonvulsants drugs (like phenobarbital, carbamazepine, ethotoin, ethosuximide, trimethadione) or if you have any other allergies before taking this drug.

Notify your doctor about your medical history especially of porphyria (certain blood conditions), diabetes, liver disease, lupus, folate or vitamin B-12 deficiency (megaloblastic anemia), alcohol use.

Avoid taking alcohol with phenytoin as it may change blood levels of phenytoin which can be dangerous. Don’t drive, use machinery, or do anything that needs sharpness until you can do it safely.

If you have diabetes, monitor your blood sugar levels as this drug may increase your blood sugar level. Inform your doctor if you find any abnormal results. Your dose needs to be adjusted.

Take vitamin D supplements to prevent osteomalacia (weakening of the bones). Discuss this with your doctor.

Discuss with your doctor about the best way to care for your teeth, gums, and mouth during your treatment with phenytoin as there is a risk of gum damage caused by phenytoin.

During pregnancy, use this drug only when the benefits outweigh the risk. It may harm the fetus. But, untreated seizures are a severe problem that can harm both mother and her fetus, do not stop using this medicine unless advised by your doctor. If you are planning a pregnancy, or become pregnant, talk to your doctor about the risk of using this drug during pregnancy. Because birth control pills, patches, implants, and injections may not work if taken with this medication. Take advice from a doctor about alternate methods of birth control.

This drug passes into breast milk. Consult your doctor before breastfeeding.

What are the drug Interactions of Phenytoin?

Drug interactions may alter how your medications act/increase your risk for dangerous side effects.

Your prescriber should manage all of your medications carefully to avoid possible drug interactions. Discuss with your doctor about all the products you are using including prescription, nonprescription drugs and vitamins/supplements.

Some medication that may interact with phenytoin includes darunavir, delavirdine, azapropazone, dofetilide, etravirine, nisoldipine, rilpivirine, colesevelam, molindone, pyridoxine (vitamin B6), orlistat, sucralfate, telithromycin.

This drug can speed up the elimination of other medications from your body, which may affect how they work. Examples of these drugs are atazanavir, corticosteroids (like prednisone), anti-cancer (like imatinib, irinotecan), cobicistat, suvorexant, theophylline, felodipine, quetiapine, quinidine, vitamin D among others.

Some drugs can affect the elimination of phenytoin from your body, and thereby changing how phenytoin works. Examples of these drugs are azole antifungals (like itraconazole), macrolide antibiotics (like erythromycin), amiodarone, estrogens, isoniazid, rifamycins (like rifabutin), anti-seizure medicines (like valproic acid), among others.

Taking phenytoin with birth control pills, patch, or ring that contain estrogen can make those pills less effective. It is better to use additional reliable birth control methods if taking these drugs together.


This drug sometimes causes a severe allergic reaction. Get emergency medical assistance if you develop symptoms like skin rash, hives, swelling of the lips, tongue, face and trouble breathing.

Phenytoin may cause severe congenital disabilities. You should use effective birth control while taking this medication.

Warnings for people with certain health conditions such as:

Liver problems: The liver metabolizes this drug. If your liver is not working well, more amount of the drug may stay in your body for a longer duration. This increases the risk for toxicity and side effects.

Diabetes: Phenytoin may increase your blood sugar levels.

Kidney problems: In case of severe kidney disease, your dose may need to be adjusted or monitored more closely.

Thyroid disease: This drug may affect your thyroid hormone levels. Discuss your thyroid condition with your doctor before you take phenytoin.

Withdrawal precipitated seizure: May precipitate status epilepticus. Reduce dose gradually.

What are the forms and strengths for Phenytoin?

Generic: Phenytoin
Form: Extended-release, oral capsule
Strengths: 100mg, 200mg, 300mg

Brand: Dilantin
Form: Extended-release, oral capsule
Strengths: 30mg, 100mg

Brand: Phenytek
Form: Extended-release, oral capsule
Strengths: 200mg, 300mg

Form: Chewable tablet
Strengths: 50mg

Form: Oral suspension
Strengths: 125mg/5mL

Form: Injectable solution
Strengths: 50mg/mL

What is the dosage of Phenytoin in adults/children?

For Seizures (epilepsy):

Adult (18–64 years):

Initial dose: 100mg orally taken three times per day.

Maintenance: 300-400mg/day; increase to 600mg/day if needed, and adjust dose no sooner than 7-10 day intervals when indicated.

Form: Suspension:

Initial dose: 125mg orally taken three times per day; increase to 625 mg/day if needed. Adjust dose no sooner than 7-10 day intervals when indicated.

Extended-release capsule:

Initial dose: 100mg capsule taken three times per day.

Maintenance dosage: 100mg capsule taken 3–4 times per day. The doctor may increase your dose to two 100mg capsules taken three times per day if needed.


Children (0–17 years):

For status epilepticus:

Initial dose:15-20mg/kg IV in single or divided dose; if necessary may administer additional dose of 5-10mg/kg 10 min after loading dose.

Maintenance: 4-8mg/kg/day IV divided twice daily.

For Controlling of Tonic-Clonic and Complex Partial Seizures:

Neonates (below 28 days):

Initial: 5-8mg/kg/day intravenous or orally divided every 8-12 hour.

Neonates (above 28 days):

Initial dosage: 5mg/kg/day in 2 divided doses in neonates.

Initial dosage: 5 mg/kg/day in 2-3 divided doses in 6 months to 16 years.

Age-based maintenance dose:

6 months-4 years: Usual range, 8-10mg/kg/day intravenous or orally divided two to three times daily.

4-7 years: Usual range, 7.5-9mg/kg/day intravenous or orally divided two to three times daily.

7-10 years: Usual range, 7-8mg/kg/day intravenous or orally divided two to three times daily.

10-16 years: Usual range, 6-7mg/kg/day intravenous or orally divided two to three times daily.

For Anticonvulsant:

5mg/kg/day orally in 2-3 divided doses, initially; may make dose adjustments no sooner than 7-10 day intervals.

Maintenance: 4-8 mg/kg/day orally; not to exceed 300mg/day; higher doses may be considered in infant and young children (range: 8-10mg/kg/day in divided doses)

5mg/kg/day orally, initially in 2-3 equally divided doses; may adjust dose no sooner than 7-10-day intervals.

Maintenance: 4-8mg/kg/day orally not to exceed 300mg/day.


TheMedPharma has made every effort to make sure that all the information is factually correct, comprehensive, and up-to-date. However, this website should not be considered as a substitute for the advice, knowledge and expertise of a licensed healthcare professional. You should always consult your doctor or licensed health care professional before taking any medication. The drug information contained herein is subjected to changes if required. The lack of warnings or other information for a given drug does not mean that the drug or its combination is safe, effective or appropriate for use in all patients.