phenytoin (redirected from Dipheninum)

phenytoin /phen·y·to·in/ (fen´ĭ-toin″) an anticonvulsant used in the control of various kinds of epilepsy and of seizures associated with neurosurgery.

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phen·y·to·in (fn-tn, f-nt-)

n.

An anticonvulsant drug chemically related to the barbiturates and used most commonly in the treatment of epilepsy.

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Phenytoin (Dilantin)

Anti-convulsive medication used to treat seizure disorders.

Mentioned in: Thyroid Function Tests

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phenytoin

[fen′ətō′in]

a drug that alters cells, membrane conductances of Na⁺ and Ca²⁺, ions whose conductances are important during the function of excitable nerve, heart, and muscle tissues.

indications It is prescribed as an anticonvulsant for the treatment and prevention of tonic-clonic seizures, complex partial seizures, and seizures resulting from head trauma or surgery. It has an unlabeled use as an antiarrhythmic agent, particularly in digitalis-induced ventricular arrhythmias. Establishing and maintaining the desired plasma concentration can be difficult because phenytoin has a high but variable amount of protein binding (typically 80%) and undergoes capacity-limited metabolism (Michaelis-Menten kinetics), with a half-life ranging from approximately 7 to 42 hrs.

contraindications Known hypersensitivity to this drug or to other hydantoins prohibits its use. It is used with caution in patients with a history of hepatic or hematologic abnormalities and in the presence of certain arrhythmias. Phenytoin has been shown to cause fetal malformations, but the benefit to risk ratio can often justify continued use during pregnancy.

adverse effects Among the more serious adverse effects are ataxia, nystagmus, hypersensitivity reactions, and gingival hyperplasia. Rarely, a variety of severe reactions occurs. This drug interacts with many other drugs.

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phenytoin [fen´ĭ-toin″]

an anticonvulsant used in the treatment of epilepsy other than the petit mal type, the treatment of status epilepticus, and the prevention and treatment of seizures associated with neurosurgery; administered orally. Called also diphenylhydantoin.

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phenytoin

an anticonvulsant used as the sodium salt. Occasionally used in the treatment of tonic-clonic and psychomotor seizures; also used for the control of cardiac arrhythmias, especially those caused by digitalis intoxication. Formerly called diphenylhydantoin.

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phenytoin (diphenylhydantoin)

Dilantin-125, Dilantin Infatabs

Pharmacologic class: Hydantoin derivative

Therapeutic class: Anticonvulsant

Pregnancy risk category D

Action

Thought to limit seizure activity by promoting sodium efflux from neurons in motor cortex and reducing activity in brainstem centers responsible for tonic phase of tonic-clonic seizures

Availability

Capsules (prompt-release): 30 mg, 100 mg

Capsules (extended-release): 30 mg, 100 mg

Injection: 50 mg/ml in 2- and 5-ml ampules

Oral suspension: 30 mg/5 ml, 125 mg/5 ml

Tablets (chewable): 50 mg

⊘Indications and dosages

➣ Status epilepticus

Adults: Loading dose of 10 to 15 mg/kg by slow I.V., then a maintenance dosage of 100 mg P.O. or I.V. q 6 to 8 hours

Neonates and children: Loading dose of 15 to 20 mg/kg I.V. in divided doses of 5 to 10 mg/kg

➣ Generalized tonic-clonic (grand mal) and complex partial (psychomotor, temporal lobe) seizures

Adults: Loading dose of 1 g P.O. (extended-release) in three divided doses (400 mg, 300 mg, and 300 mg) at 2-hour intervals in hospitalized patients requiring rapid steady-state serum levels (when I.V. route isn't desired). Maintenance dosing usually starts 24 hours after loading dose. Patients who haven't had previous treatment usually start at 100 mg (125 mg suspension) P.O. t.i.d., adjusted as needed to a maximum of 600 mg (625 mg suspension) P.O. daily. Alternatively, if divided doses control seizures, one daily dose of 300 mg P.O. (extended-release phenytoin sodium).

Children: Initially, 5 mg/kg/day P.O. in two or three equally divided doses; maintenance dosage individualized and given in two to three divided doses (not to exceed 300 mg/day).

➣ To prevent seizures during neurosurgery

Adults: 100 to 200 mg I.M. at 4-hour intervals

Off-label uses

• Arrhythmias
• Severe preeclampsia
• Trigeminal neuralgia
• Recessive dystrophic epidermolysis bullosa, junctional epidermolysis bullosa

Contraindications

• Hypersensitivity to drug
• Sinus bradycardia, sinoatrial block, second- or third-degree atrioventricular block, Adams-Stokes syndrome

Precautions

Use cautiously in:
• hepatic disease, diabetes mellitus, skin rash
• pregnant or breastfeeding patients (safety not established).

Administration

• Before I.V. use, check designated line for patency and flush with normal saline solution. Deliver no faster than 50 mg/minute for adults or 1 to 3 mg/kg/minute in children and neonates; then flush with normal saline solution. Avoid extravasation (can cause severe tissue damage).
☞ Don't administer I.V. into dorsal hand veins, because purple glove syndrome may occur.
• When giving oral solution through nasogastric tube, dilute dose with sterile water or normal saline solution; after administration, flush tube with at least 20 ml of diluent.
• Withhold enteral feedings for at least 1 hour before and 1 hour after oral administration.
• Give I.M. only as last resort (may cause pain and reduce drug absorption).
• Know that patients with history of renal or hepatic disease should not receive P.O. loading dose.

Route	Onset	Peak	Duration
P.O.	Unknown	3 hr	6-12 hr
P.O. (extended)	Unknown	4-12 hr	12-36 hr
I.V.	Unknown	Rapid	12-24 hr
I.M.	Unknown	Erratic	12-24 hr

Adverse reactions

CNS: headache, fatigue, dizziness, drowsiness, weakness, depression, ataxia, slurred speech, confusion, agitation, dysarthria, dyskinesia, extrapyramidal symptoms, insomnia, irritability, twitching, nervousness, numbness, psychotic disturbances, tremor, CNS depression (with I.V. use), coma

CV: vasodilation, edema, chest pain, tachycardia, hypotension (increased with I.V. use), cardiovascular collapse (with I.V. use)

EENT: diplopia, amblyopia, nystagmus, visual field defect, eye pain, conjunctivitis, photophobia, mydriasis, hearing loss, tinnitus, ear pain, epistaxis, rhinitis, sinusitis, pharyngitis

GI: nausea, vomiting, diarrhea, constipation, lip enlargement, dry mouth

GU: pink, red, or reddish-brown urine; gynecomastia; Peyronie's disease

Hepatic: jaundice, toxic hepatitis, hepatic damage

Hematologic: macrocytosis, simple anemia, megaloblastic anemia, monocytosis, leukocytosis, hemolytic anemia, thrombocytopenia, agranulocytosis, granulocytopenia, leukopenia, pancytopenia

Metabolic: hypocalcemia, diabetes insipidus, hyperglycemia

Musculoskeletal: back pain, pelvic pain, osteomalacia

Respiratory: dyspnea, increased cough and sputum, pneumonia, hyperventilation, hypoxia, hemoptysis, bronchitis, apnea, asthma, aspiration pneumonia, pulmonary fibrosis, atelectasis, pneumothorax

Skin: rash, pruritus, bruising, exfoliative dermatitis, hypertrichosis, hirsutism, alopecia, Stevens-Johnson syndrome

Other: gingival hyperplasia, altered taste, fever, lymphadenopathy, weight gain or loss, injection site reaction, coarsened facial features, lupus erythematosus syndrome, allergic reactions

Interactions

Drug-drug. Acetaminophen, amiodarone, carbamazepine, cardiac glycosides, corticosteroids, dicumarol, disopyramide, doxycycline, estrogens, haloperidol, hormonal contraceptives, methadone, metapyrone, mexiletine, quinidine, theophylline, valproic acid: increased metabolism and decreased effects of these drugs

Activated charcoal, antacids, sucralfate: decreased phenytoin absorption

Allopurinol, amiodarone, benzodiazepines, chloramphenicol, chlorpheniramine, cimetidine, disulfiram, fluconazole, ibuprofen, isoniazid, metronidazole, miconazole, omeprazole, phenacemide, phenothiazines, phenylbutazone, salicylates, succinimides, sulfonamides, tricyclic antidepressants, trimethoprim, valproic acid: increased phenytoin effects

Antineoplastics, barbiturates, carbamazepine, diazoxide, folic acid, influenza vaccine, loxapine, nitrofurantoin, pyridoxine, rifampin, theophylline: decreased phenytoin effects

Cyclosporine, dopamine, furosemide, levodopa, levonorgestrel, mebendazole, muscle relaxants, nondepolarizing phenothiazines, sulfonylureas: decreased effects of these drugs

Drug-diagnostic tests. Alkaline phosphatase, eosinophils, gamma-glutamyltransferase, glucose: increased levels

Dexamethasone (1-mg) suppression test, metyrapone test: interference with test results

Free thyroxine, serum thyroxine: decreased levels

Drug-food. Enteral tube feedings: decreased phenytoin absorption

Folic acid: decreased folic acid absorption

Drug-behaviors. Acute alcohol ingestion: increased phenytoin blood level

Chronic alcohol ingestion: decreased phenytoin blood level

Patient monitoring

• Assess blood pressure, ECG, and heart rate, especially during I.V. loading dose. Watch for adverse reactions.
• Monitor phenytoin blood level; therapeutic range is 10 to 20 mcg/ml.
• Evaluate CBC and kidney and liver function tests.
• Closely monitor prothrombin time and Internationalized Normal Ratio in patients receiving warfarin concurrently.
• Monitor drug efficacy.

Patient teaching

• Explain drug therapy, need for follow-up tests, and importance of taking drug exactly as prescribed.
• Caution patient not to stop therapy abruptly.
• Advise patient to avoid alcohol.
☞ Instruct patient to report rash immediately.
• Inform patient that drug may discolor urine.
• Tell female patient drug may make hormonal contraceptives ineffective.
• Instruct patient to practice good dental hygiene to minimize gingival hyperplasia.
• Encourage patient to seek medical advice before taking over-the-counter preparations.
• As appropriate, review all other significant and life-threatening adverse reactions and interactions, especially those related to the drugs, tests, foods, and behaviors mentioned above.

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phenytoin

Dilantin® Pharmacology An antiepileptic and anticonvulsant widely used as a monotherapy for partial seizures–eg, 2º generalized seizures. See Imipramine, Seizures, Therapeutic drug monitoring.