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Drug Name:


Generic Name and Formulations:
Fosphenytoin sodium (prodrug of phenytoin) 75mg/mL (equivalent to 50mg/mL phenytoin sodium); soln for IV or IM inj.

Pfizer Inc.

Therapeutic Use:

Indications for CEREBYX:

Control of generalized tonic-clonic status epilepticus. Seizure prophylaxis and treatment in neurosurgery. Short-term substitution for oral phenytoin. Use only when oral phenytoin administration is not possible.


Must prescribe and dispense fosphenytoin sodium inj doses, infusion rates and concentration in dosing solutions expressed as phenytoin sodium equivalents (PE); see full labeling. Max infusion rate: 150mg PE/min. Status epilepticus: loading dose: 15–20mg PE/kg IV administered at 100–150mg PE/min; nonemergent loading dose: 10–20mg PE/kg IV or IM inj; maintenance dose: initially 4–6mg PE/kg/day. Substitution for oral phenytoin: give same total daily dose by IM or IV.


Not established.


Sinus bradycardia, sinoatrial block, or 2nd and 3rd degree A-V block. Adams-Stokes syndrome. Concomitant delavirdine.


Increased risk of SJS/TEN if HLA-B*1502 positive (esp. in Asians); avoid as an alternative for carbamazepine. Do not make adjustments in recommended doses when substituting fosphenytoin sodium injection for phenytoin sodium or vice versa. Hypotension and severe myocardial insufficiency; monitor cardiac function during and after administration; reduce or discontinue drug if needed. Hepatic or renal impairment. Phosphate restricted. Hypoalbuminemia. Porphyria. Diabetes. Monitor respiratory function during therapy; and phenytoin serum levels upon complete conversion to phenytoin (approx. 2hrs after IV or 4hrs after IM). Adjust dose gradually. Avoid abrupt cessation. Alcoholics. Slow metabolizers. Elderly (use lower dose). Debilitated. Pregnancy (Cat.D; see full labeling). Nursing mothers: not recommended.

Pharmacological Class:



Potentiated by acute alcohol intake, amiodarone, antiepileptics, azoles, capecitabine, chloramphenicol, chlordiazepoxide, cimetidine, diazepam, dicumarol, disulfiram, estrogens, ethosuximide, fluoxetine, H2-antagonists, fluvoxamine, methylphenidate, halothane, isoniazid, methylphenidate, phenothiazines, phenylbutazone, salicylates, succinimides, sulfonamides, tolbutamide, trazodone. Antagonized by chronic alcohol abuse, carbamazepine, reserpine, bleomycin, carboplatin, cisplatin, doxorubicin, methotrexate, ritonavir, St. John's wort, theophylline, vigabatrin. Antagonize azoles, corticosteroids, coumarin, doxycycline, estrogens, furosemide, oral contraceptives, rifampin, quinidine, theophylline, vitamin D, HIV antivirals (eg, amprenavir, efavirenz, lopinavir/ritonavir, indinavir, nelfinavir, ritonavir, saquinavir), antiepileptics, atorvastatin, others. Variable effects with phenobarbital, valproic acid, and sodium valproate. Concomitant tricyclic antidepressants may precipitate seizures. Concomitant fosamprenavir/ritonavir may potentiate amprenavir. Variable PT/INR responses with concomitant warfarin. Concomitant neuromuscular blockers (eg, pancuronium, vecuronium, rocuronium, cisatracurium); may need higher infusion rate. Caution with drugs that are highly bound to serum albumin. May decrease T4 serum concentrations, or produce low results in dexamethasone or metyrapone tests. May increase serum concentrations of glucose, alkaline phosphatase and gamma glutamyl transpeptidase.

Adverse Reactions:

Nystagmus, dizziness, pruritus, paresthesia, headache, somnolence, ataxia, tinnitus, nausea, cardiovascular collapse, CNS depression, hypotension (esp. after high doses or rapid IV), atrial and ventricular conduction depression, ventricular fibrillation, DRESS, multiorgan hypersensitivity, rash (eg, Stevens-Johnson syndrome, toxic epidermal necrolysis; discontinue if occurs), hepatotoxicity (discontinue immediately; do not readminister), blood dyscrasias, lymphadenopathy, hyperglycemia, lowering of serum folate levels, bradycardia, others.

Generic Availability:


How Supplied:

Vials 100mg PE/2mL—1, 25; 500mg PE/10mL—1, 10

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