Phenytoin is used for the management and prevention of certain types of seizures, as well as for the prevention and treatment of seizures that occur during or following neurosurgery. It works on the brain to reduce the number and severity of seizures.

Your doctor may have suggested this medication for conditions other than the ones listed in these drug information articles. If you have not discussed this with your doctor or are not sure why you are taking this medication, speak to your doctor. Do not stop taking this medication without consulting your doctor.

The recommended dose of phenytoin varies according to individual needs. The usual adult dose is 300 mg to 400 mg daily taken by mouth in divided doses or a single dose. An increase to 600 mg taken in divided doses may be needed in some cases. The children's dose is based on age and body weight. The level of phenytoin in your blood can be checked through laboratory testing. This test helps your doctor determine the dose of phenytoin that best suits you.

Phenytoin may be taken with or without food. Do not use capsules that are discoloured.

Many things can affect the dose of medication that a person needs, such as body weight, other medical conditions, and other medications. If your doctor has recommended a dose different from the ones listed here, do not change the way that you are taking the medication without consulting your doctor.

It is very important that this medication be taken exactly as prescribed by your doctor. If you miss a dose, take it as soon as possible and continue on with your regular schedule. If it is almost time for your next dose, skip the missed dose and continue on with your regular dosing schedule. Do not double doses unless advised to do so by your doctor.

Dilantin^® is available in capsule, Infatab (tablet), and liquid form.

Capsules:
30 mg: Each white capsule with pink cap, imprinted "Parke-Davis" and "P-D 30" in black ink, contains phenytoin 30 mg. Nonmedicinal ingredients: lactose, magnesium stearate, sugar, and talc; capsule shell: D&C Yellow No. 10, FD&C Red No. 3, gelatin, and titanium dioxide. Sodium: <1 mmol (2.52 mg).
100 mg: Each white capsule with orange cap, imprinted "Parke-Davis" and "P-D 100" in black ink, contains phenytoin 100 mg. Nonmedicinal ingredients: lactose, magnesium stearate, sugar, and talc; capsule shell: FD&C Yellow No. 6, gelatin, and titanium dioxide. Sodium: <1 mmol (8.39 mg).

Dilantin Infatabs: Each flavoured, triangular, grooved tablet contains phenytoin 50 mg. Nonmedicinal ingredients: alcohol, magnesium stearate, spearmint oil, sugar, and talc.

Liquid:
Dilantin-30 Pediatric: Each 5 mL of flavoured, coloured suspension contains phenytoin 30 mg. Nonmedicinal ingredients: alcohol, banana oil, citric acid, glycerin, magnesium aluminum silicate, orange oil, polysorbate 40, FD&C Red No. 2, sodium benzoate, sodium carboxymethylcellulose, sugar, vanillin, and FD&C Yellow No. 6.
Dilantin-125: Each 5 mL of flavoured, coloured suspension contains phenytoin 125 mg. Nonmedicinal ingredients: alcohol, banana oil, citric acid, glycerin, magnesium aluminum silicate, orange oil, polysorbate 40, sodium benzoate, sodium carboxymethylcellulose, sugar, vanillin, and FD&C Yellow No. 6.

The side effects listed below are not experienced by everyone who takes this medication. If you are concerned about side effects, discuss the risks and benefits of this medication with your doctor. Your health professional may be able to help you to deal with some of the effects.

The following side effects may go away as your body becomes used to the medicine; check with your doctor if the following side effects continue or become bothersome.

More common
• constipation
• dizziness (mild)
• drowsiness (mild)

Less common
• difficulty sleeping
• enlargement of jaw
• muscle twitching
• swelling of breasts (likely to be more noticeable in men)
• thickening of lips
• unusual and excessive hair growth on body and face
• widening of nose tip

Contact your doctor as soon as possible if any of the following side effects occur:

More common
• bleeding, tender, or enlarged gums
• blurred or double vision (may indicate the need for a lower dose)
• clumsiness or unsteadiness
• confusion
• continuous, uncontrollable eye movements (may indicate the need for a lower dose)
• fever
• headache
• muscle pain
• skin rash or itching
• slurred speech or stuttering (may indicate the need for a lower dose)
• sore throat
• swollen glands in neck or underarms
• trembling (may indicate the need for a lower dose)
• unusual excitement, nervousness, or irritability

Symptoms of too much medication
• blurred or double vision
• clumsiness or unsteadiness (severe)
• confusion (severe)
• dizziness or drowsiness (severe)
• seizures
• staggering walk
• stuttering or slurred speech

Some people may experience side effects other than those listed. Check with your doctor if you notice any symptom that worries you while you are taking this medication.

Dental hygiene: The importance of good dental hygiene is stressed in order to minimize the development of gingival hyperplasia (swollen and bleeding gums) and its complications.

Diabetes: High blood sugar with the use of phenytoin has been reported. Phenytoin may have an effect on the action of medications used to lower blood sugar for people with diabetes. People who have diabetes should monitor their blood sugar more closely when starting or stopping phenytoin treatment.

Hypersensitivity syndrome: A severe allergic reaction called hypersensitivity syndrome has occurred for some people with the use of phenytoin. Contact your doctor or pharmacist if you experience any of the following:

• fever
• joint pain
• malaise
• serious rashes
• swelling of lymph glands
• upset stomach
• vomiting

Liver function: Some people have reported liver problems with the use of phenytoin. These cases have been associated with an allergic reaction that includes fever, skin rashes or hives, or swollen lymph glands. The reaction usually occurs within the first two months of treatment.

Other medications: People taking phenytoin should consult with their doctor or pharmacist before taking any other medications, or alcoholic beverages.

Regular dosing: People taking phenytoin should be very aware of the importance of taking the medication exactly as prescribed and of informing their doctor of any condition which prevents them from taking the medication as prescribed (e.g., surgery, illness, difficulty swallowing).

Skin rash: The development of skin rashes of varying severity has been reported. People taking phenytoin should call their doctor if a skin rash appears.

Withdrawal of medication: People who have epilepsy should not stop taking phenytoin without consulting their doctor, as this may result in an increase in the number or severity of seizures.

Pregnancy: The use of phenytoin during pregnancy requires that the benefits of treatment be weighed against the risks.

The following agents may affect how phenytoin works or increase the risk of side effects:

Phenytoin may affect the way the following medications work:

If you are taking any of these medications, speak with your doctor or pharmacist. Depending on your specific circumstances, your doctor may want you to:

• stop taking one of the medications,
• change one of the medications to another,
• change how you are taking one or both of the medications, or
• leave everything as is.

An interaction between two medications does not always mean that you must stop taking one of them. In many cases, interactions are intended or are managed by close monitoring. Speak to your doctor about how any drug interactions are being managed or should be managed.

Medications other than those listed above may interact with this medication. Tell your doctor or prescriber about all prescription, over-the-counter (non-prescription), and herbal medications that you are taking. Also tell them about any supplements you take. Since caffeine, alcohol, the nicotine from cigarettes, or street drugs can affect the action of many medications, you should let your prescriber know if you use them.