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Last reviewed on RxList: 4/30/2019
Phenytek Side Effects Center

Medical Editor: John P. Cunha, DO, FACOEP

Last reviewed on RxList 4/30/2019

Phenytek (extended phenytoin sodium capsule) is an antiepileptic drug indicated for the control of generalized tonic-clonic (grand mal) and psychomotor (temporal lobe) seizures and prevention and treatment of seizures occurring during or following neurosurgery. Common side effects of Phenytek include:

Antiepileptic drugs (AEDs), including Phenytek, increase the risk of suicidal thoughts or behavior. Tell your doctor if this occurs while taking Phenytek.

Patients who have received no previous treatment may be started on one 100 mg extended Phenytek capsule three times daily and the dosage then adjusted to suit individual requirements. Phenytek may interact with alcohol, amiodarone, other anti-epileptic drugs, azoles, capecitabine, chloramphenicol, chlordiazepoxide, diazepam, disulfiram, estrogens, fluorouracil, fluoxetine, fluvastatin, fluvoxamine, H2-antagonists, halothane, isoniazid, methylphenidate, omeprazole, phenothiazines, salicylates, sertraline, succinimides, sulfonamides, ticlopidine, tolbutamide, trazodone, warfarin, anticancer drugs usually in combination, carbamazepine, diazepam, diazoxide, folic acid, fosamprenavir, nelfinavir, reserpine, rifampin, ritonavir, St. John's Wort, sucralfate, theophylline, vigabatrin, some supplements or antacids (containing calcium carbonate, aluminum hydroxide, and magnesium hydroxide), neuromuscular blocking agents, phenobarbital, sodium valproate, and valproic acid. Tell your doctor all medications and supplements you use. Tell your doctor if you are pregnant or plan to become pregnant while taking Phenytek; it may harm a fetus. Pregnant patients taking Phenytek are advised to enroll in the North American Antiepileptic Drug (NAAED) Pregnancy Registry. Phenytek passes into breast milk. Breastfeeding while taking Phenytek is not recommended. Abrupt withdrawal of Phenytek in epileptic patients may precipitate status epilepticus.

Our Phenytek Capsule (extended phenytoin sodium capsule) Side Effects Drug Center provides a comprehensive view of available drug information on the potential side effects when taking this medication.

This is not a complete list of side effects and others may occur. Call your doctor for medical advice about side effects. You may report side effects to FDA at 1-800-FDA-1088.


Epilepsy: Symptoms, Causes and Treatment See Slideshow
Phenytek Professional Information


Body as a Whole

Allergic reactions in the form of rash and rarely more serious forms (see Skin and Appendages paragraph below) and DRESS (see WARNINGS) have been observed. Anaphylaxis has also been reported.

There have also been reports of coarsening of facial features, systemic lupus erythematosus, periarteritis nodosa, and immunoglobulin abnormalities.

Nervous System

The most common adverse reactions encountered with phenytoin therapy are nervous system reactions and are usually dose-related. Reactions include nystagmus, ataxia, slurred speech, decreased coordination, somnolence, and mental confusion. Dizziness, vertigo, insomnia, transient nervousness, motor twitchings, paresthesias, and headaches have also been observed. There have also been rare reports of phenytoin-induced dyskinesias, including chorea, dystonia, tremor, and asterixis, similar to those induced by phenothiazine and other neuroleptic drugs.

A predominantly sensory peripheral polyneuropathy has been observed in patients receiving long-term phenytoin therapy.

Digestive System

Acute hepatic failure, toxic hepatitis, liver damage, nausea, vomiting, constipation, enlargement of the lips, and gingival hyperplasia.

Skin and Appendages

Dermatological manifestations sometimes accompanied by fever have included scarlatiniform or morbilliform rashes. A morbilliform rash (measles-like) is the most common; other types of dermatitis are seen more rarely. Other more serious forms which may be fatal have included bullous, exfoliative or purpuric dermatitis, Stevens-Johnson syndrome, and toxic epidermal necrolysis (see WARNINGS). There have also been reports of hypertrichosis.

Hematologic and Lymphatic System

Hematopoietic complications, some fatal, have occasionally been reported in association with administration of phenytoin. These have included thrombocytopenia, leukopenia, granulocytopenia, agranulocytosis, and pancytopenia with or without bone marrow suppression. While macrocytosis and megaloblastic anemia have occurred, these conditions usually respond to folic acid therapy. Lymphadenopathy including benign lymph node hyperplasia, pseudolymphoma, lymphoma, and Hodgkin's disease have been reported (see WARNINGS).

Special Senses

Altered taste sensation including metallic taste.


Peyronie's disease.

Read the entire FDA prescribing information for Phenytek (Phenytoin Sodium)


If you have had a seizure, it means you have epilepsy. See Answer
Related Resources for Phenytek

Drug Comparison

© Phenytek Patient Information is supplied by Cerner Multum, Inc. and Phenytek Consumer information is supplied by First Databank, Inc., used under license and subject to their respective copyrights.


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