Dilantin Side Effects

Generic name: phenytoin

Note: This document contains side effect information about phenytoin. Some of the dosage forms listed on this page may not apply to the brand name Dilantin.

Some side effects of Dilantin may not be reported. Always consult your doctor or healthcare specialist for medical advice. You may also report side effects to the FDA.

For the Consumer

Applies to phenytoin: oral capsule extended release, oral suspension, oral tablet chewable

Get emergency medical help if you have any of these signs of an allergic reaction while taking phenytoin (the active ingredient contained in Dilantin) hives; difficulty breathing; swelling of your face, lips, tongue, or throat. You may be more likely to have an allergic reaction if you are African-American.

Report any new or worsening symptoms to your doctor, such as: mood or behavior changes, depression, anxiety, or if you feel agitated, hostile, restless, hyperactive (mentally or physically), or have thoughts about suicide or hurting yourself.

Call your doctor at once if you have a serious side effect such as:

• fever, swollen glands, body aches, flu symptoms;

• skin rash, easy bruising or bleeding, severe tingling, numbness, pain, muscle weakness;

• upper stomach pain, loss of appetite, dark urine, jaundice (yellowing of the skin or eyes);

• chest pain, irregular heart rhythm, feeling short of breath;

• confusion, nausea and vomiting, swelling, rapid weight gain, urinating less than usual or not at all;

• new or worsening cough with fever, trouble breathing;

• tremor (uncontrolled shaking), restless muscle movements in your eyes, tongue, jaw, or neck;

• patchy skin color, red spots, or a butterfly shaped skin rash over your cheeks and nose (worsens in sunlight); or

• severe skin reaction -- fever, sore throat, swelling in your face or tongue, burning in your eyes, skin pain, followed by a red or purple skin rash that spreads (especially in the face or upper body) and causes blistering and peeling.

Less serious side effects of phenytoin may include:

• slurred speech, loss of balance or coordination;

• swollen or tender gums; or

• headache, dizziness, nervousness, or sleep problems (insomnia).

This is not a complete list of side effects and others may occur. Call your doctor for medical advice about side effects.

For Healthcare Professionals

Applies to phenytoin: compounding powder, injectable solution, oral capsule, oral capsule extended release, oral suspension, oral tablet chewable

Nervous system

Nervous system effects are common and frequently dose-dependent. Nystagmus, ataxia, slurred speech, impaired cognition, and diplopia frequently occur. At higher plasma levels, drowsiness, lethargy, and coma may occur.

Chronic administration may result in memory impairment, intellectual decline, and irritability. These effects are frequently subtle. Psychiatric illness (including mania and psychosis), headaches, dyskinesias (including chorea, dystonia, and tremor), benign intracranial hypertension, opsoclonus, ophthalmoplegia, sensory polyneuropathy, cerebellar degeneration, myoclonus, parkinsonism, and asterixis have also been reported less frequently.

The pathologic characteristics of phenytoin-induced neuropathy include axonal shrinkage and secondary demyelination.

At very high plasma levels, phenytoin may rarely precipitate seizures and/or status epilepticus.

Other

Abrupt discontinuation in epileptic patients may precipitate worsening of seizures and status epilepticus. Additionally, phenytoin (the active ingredient contained in Dilantin) may exacerbate preexisting lupus.

Other side effects have included tibial and facial edema, altered taste, coarsening of facial features, systemic lupus erythematosus, periarteritis nodosa, and immunoglobulin abnormalities.

Local

Local side effects have included edema, discoloration, and pain of the distal limb (described as "purple glove syndrome") following peripheral IV phenytoin (the active ingredient contained in Dilantin) injection. This may or may not be associated with extravasation. Although resolution of symptoms may be spontaneous, skin necrosis and limb ischemia have occurred and required such interventions as fasciotomies, skin grafting and amputation.

Cardiovascular

Cardiovascular side effects include hypotension, bradycardia, other arrhythmias and cardiac arrest rarely. These complications are most likely to occur in patients receiving parenteral phenytoin (the active ingredient contained in Dilantin) or in patients with underlying cardiovascular disease.

Phenytoin has been implicated as a possible cause of myocarditis related to drug hypersensitivity.

Hypersensitivity

Hypersensitivity side effects have been reported. Phenytoin is the most common cause of the anticonvulsant hypersensitivity syndrome. A variety of hypersensitivity reactions have been reported in association with phenytoin (the active ingredient contained in Dilantin) use. Reactions frequently involve generalized rashes, eosinophilia, fever, lymphadenopathy, and hepatic derangements. Myopathy, rhabdomyolysis, renal dysfunction, disseminated intravascular coagulation, and purpura fulminans have also been reported to occur as part of a phenytoin hypersensitivity reaction.

The constellation of findings which includes lymphadenopathy, fever, exfoliative dermatitis, eosinophilia and hepatic damage is often called "pseudolymphoma" and may be fatal.

One study has suggested that hypersensitivity to phenytoin may occur in a familial pattern.

Hepatic

The more serious hepatic effects have often been reported in association with hypersensitivity reactions.

Hepatic side effects including elevated liver function tests, acute hepatitis, chronic persistent hepatitis, cholestasis and fulminant hepatic failure have all been reported. Mild enzyme elevation is common and often represents enzyme induction and not hepatic pathology.

Dermatologic

One study of the occurrence of subacute local cutaneous reactions in patients receiving IV phenytoin (the active ingredient contained in Dilantin) reported that 29 out of 115 patients (25.2%) had such reactions. These included 22 mild reactions and 7 moderate reactions.

Erythema multiforme is more likely if the patient is receiving concomitant X-ray therapy.

Dermatologic side effects including Stevens-Johnson syndrome, toxic epidermal necrolysis, pemphigus vulgaris, erythema multiforme, a pseudonymous fungoides syndrome, erythroderma, facial pustules, hyperpigmentation, coarsening of facial features, hirsutism, hypertrichosis (which is occasionally irreversible), and lupus-like symptoms have been reported. A case of acquired acromelanosis has been reported. Another case report has suggested that phenytoin may cause an erythematous lichenified rash of the lips.

Respiratory

Cases of an acute pulmonary disease (which may be part of a hypersensitivity angiitis) have been reported following treatment with phenytoin (the active ingredient contained in Dilantin) Pathologically, the disease has been described both as an interstitial pneumonitis and as a lymphocytic interstitial pneumonia.

Respiratory side effects including life-threatening respiratory depression may occur, particularly during acute intoxication or following rapid intravenous dosing, especially with concomitant administration of benzodiazepines and barbiturates.

Oncologic

Oncologic side effects have included cases of increased frequency of malignancy (particularly Hodgkin's and non-Hodgkin's lymphoma and lung cancer) in patients taking phenytoin (the active ingredient contained in Dilantin) and other antiepileptic medications. Other investigators have not found an association with malignancy.

Hematologic

Hematologic side effects including bone marrow suppression, agranulocytosis, thrombocytopenia, pure red cell aplasia, and prothrombin deficiency have been reported rarely.

A reversible IgA deficiency has been reported. Several case reports have suggested that phenytoin may rarely induce panhypogammaglobulinemia. Another case report has suggested that phenytoin may cause a permanent deficiency in B cell immunity.

Other case reports suggest that phenytoin may cause bone marrow granulomata formation.

Immunologic

One report has suggested that phenytoin (the active ingredient contained in Dilantin) therapy may be associated with the development of sarcoidosis. However, a clear relationship between sarcoidosis and phenytoin therapy has not been established.

The systemic granulomatous vasculitis associated with phenytoin requires discontinuation of phenytoin and high-dose steroid therapy.

Immunologic side effects including a lupus-like syndrome associated with the presence of lupus anticoagulant may occur. Cases of a systemic granulomatous vasculitis and necrotizing angiitis have been reported.

Renal

Renal side effects including nephrotic syndrome and interstitial nephritis have been reported in association with phenytoin (the active ingredient contained in Dilantin) therapy.

Endocrine

Phenytoin increases the rate of T4 and T3 metabolism and may lead to hypothyroidism in patients with hypothyroidism who are being treated with T4. Phenytoin may also cause a 20% to 40% decrease in serum total and free T4 concentrations and a smaller decrease in serum total and free T3 concentrations in patients who have no thyroid disease.

Additionally, the presence of diabetes mellitus (both types I and II) has been associated with alterations in the pharmacokinetic disposition of phenytoin (the active ingredient contained in Dilantin) Decreases in plasma protein binding, Vmax and Vmax/Km have been reported. (Km is the serum concentration at which 50% saturation occurs and Vmax is the maximum rate of metabolism.) As a result, lower steady-state concentration of phenytoin may occur in patients with diabetes mellitus.

Endocrine effects include glucose intolerance and decreases in serum T4 and FT4. Favorable changes in lipid profiles have also been reported and include elevated HDL cholesterol and lower LDL cholesterol. Increases in serum estradiol levels have been reported and may contribute to the sexual dysfunction which may occur in males treated with phenytoin. Gynecomastia has also been reported. Alterations in vitamin D metabolism have been reported in patients taking phenytoin and other anticonvulsants. Hypocalcemia and osteomalacia have been reported.

Gastrointestinal

Salivary gland hypertrophy has also been reported. A single case of drug-induced esophageal stricture has been reported.

Gastrointestinal side effects including gingival hyperplasia (in as many as 50% of treated patients) have been reported. The gingival hyperplasia associated with phenytoin is occasionally severe enough to merit surgical removal. Nausea, vomiting, and constipation have been reported.

Musculoskeletal

Musculoskeletal side effects including myopathy in association with anticonvulsant osteomalacia has been reported in patients taking phenytoin (the active ingredient contained in Dilantin)

Genitourinary

Genitourinary side effects have included Peyronie disease, male sexual dysfunction and, more rarely, priapism has been associated with phenytoin (the active ingredient contained in Dilantin) therapy.

Metabolic

Metabolic side effects associated with phenytoin (the active ingredient contained in Dilantin) therapy may include significantly reduced serum and red blood cell folate levels.

Ocular

Ocular side effects including cataracts have been reported. Several human case reports and animal studies have suggested that phenytoin (the active ingredient contained in Dilantin) may predispose patients to the development of presenile cataracts. Chronic conjunctivitis has also been reported.

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