fosphenytoin sodium

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fosphenytoin sodium

Cerebyx, Pro-Epanutin (UK)

Pharmacologic class: Hydantoin

Therapeutic class: Anticonvulsant

Pregnancy risk category D


Thought to regulate neuronal membrane by promoting sodium excretion from neurons. This action prevents hyperexcitability and excessive stimulation, which inhibits spread of seizure activity. Lacks general CNS depressant effect.


Injection: 150 mg in 2-ml vials (100 mg phenytoin sodium), 750 mg in 10-ml vials (500 mg phenytoin sodium)

Indications and dosages

Status epilepticus

Adults: 15 to 20 mg phenytoin sodium equivalent (PE)/kg I.V. at 100 to 150 mg PE/minute as a loading dose, then 4 to 6 mg (PE)/kg I.V. daily for maintenance

To prevent seizures during neurosurgery

Adults: 10 to 20 mg PE/kg I.M. or I.V. as a loading dose, then 4 to 6 mg PE/kg I.M. or I.V. daily for maintenance

Dosage adjustment

• Hepatic disease

• Renal impairment

• Elderly patients


• Hypersensitivity to drug

• Adams-Stokes syndrome

• Arrhythmias


Use cautiously in:

• hepatic or renal impairment, severe cardiac or respiratory disease

• elderly patients

• pregnant or breastfeeding patients (safety not established).


• Know that drug is a phenytoin prodrug and is given in PE units to avoid the need to perform molecular weight-based adjustments when converting between fosphenytoin and phenytoin sodium doses.

• For I.V. use, dilute in dextrose 5% in water or normal saline solution.

• Don't give faster than 150 mg PE/minute. Too-rapid infusion causes hypotension.

Check ECG, vital signs, and overall patient status continuously during infusion and for 10 to 20 minutes afterward.

• When giving I.M., rotate injection sites.

Adverse reactions

CNS: ataxia, agitation, dizziness, drowsiness, dysarthria, dyskinesia, speech disorder, extrapyramidal syndrome, headache, nervousness, weakness, confusion, hyperesthesia, paresthesia, cerebral edema, coma, intracranial hypertension

CV: hypotension, tachycardia

EENT: diplopia, nystagmus, tinnitus

GI: nausea, vomiting, constipation, dry mouth, anorexia

GU: pink, red, or reddish-brown urine

Hematologic: lymphadenopathy, aplastic anemia, agranulocytosis, leukopenia, megaloblastic anemia, thrombocytopenia

Hepatic: hepatitis

Metabolic: hypocalcemia, hypokalemia, hyperglycemia, increased glucose tolerance

Musculoskeletal: back or pelvic pain, osteomalacia

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

Other: gingival hyperplasia, altered taste, fever, facial edema, weight loss, injection site pain, allergic reactions


Drug-drug. Amiodarone, benzodiazepines, chloramphenicol, cimetidine, disulfiram, estrogens, felbamate, fluconazole, fluoxetine, halothane, influenza vaccine, isoniazid, itraconazole, ketoconazole, methylphenidate, miconazole, omeprazole, phenothiazines, phenylbutazone, salicylates, sulfonamides, tolbutamide, trazodone: increased fosphenytoin blood level

Antidepressants, antihistamines, opioids, sedative-hypnotics: additive CNS depression

Barbiturates, carbamazepine, reserpine: decreased fosphenytoin blood level

Corticosteroids, cyclosporine, doxycycline, estrogens, felbamate, methadone, quinidine, rifampin: altered effects of these drugs

Dopamine: additive hypotension

Lidocaine, propranolol: additive cardiac depression

Streptozocin, theophylline: decreased efficacy of these drugs

Warfarin: initial increase in warfarin effects in patients stabilized on warfarin therapy, followed by decreased response to warfarin

Drug-diagnostic tests. Alkaline phosphatase, glucose, hepatic enzymes: increased levels

Dexamethasone, metyrapone: test interference

Glucose tolerance test: decreased tolerance

Potassium, thyroxine: decreased levels

Thyroid function tests: decreased values

Drug-behaviors. Acute alcohol ingestion: increased drug blood level, additive CNS depression

Chronic alcohol ingestion: decreased drug blood level

Patient monitoring

• Be prepared to slow administration or stop therapy if significant cardiovascular reactions occur.

• Monitor neurologic status carefully, especially for evidence of increasing intracranial pressure.

Assess for rash. Withhold drug and notify prescriber if it occurs.

• Monitor phenytoin blood level after drug has metabolized to phenytoin (about 2 hours after I.V. dose or 4 hours after I.M. dose).

• Monitor electrolyte levels.

• Evaluate blood glucose level. Watch for hyperglycemia in patients with diabetes.

Patient teaching

• Inform patient that he may experience sensory disturbances during I.V. administration.

Advise patient to immediately report adverse effects, particularly rash.

• Tell patient that drug may turn his urine pink, red, or reddish brown.

• As appropriate, review all other significant and life-threatening adverse reactions and interactions, especially those related to the drugs, tests, and behaviors mentioned above.

McGraw-Hill Nurse's Drug Handbook, 7th Ed. Copyright © 2013 by The McGraw-Hill Companies, Inc. All rights reserved

fosphenytoin sodium

A drug used to treat STATUS EPILEPTICUS and to prevent seizures following neurosurgery and head injury. A brand name is Pro-epanutin.
Collins Dictionary of Medicine © Robert M. Youngson 2004, 2005
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