Contents

Search

fosphenytoin (Cerebyx)

Tradename: Cerebyx. Indications: - generalized tonic clonic seizures - partial seizures - status epilepticus [6] - one of the advantages of fosphenytoin is faster loading than with phenytoin Contraindications: Caution: 1) use with caution in patients with severe cardiovascular, hepatic or renal disease, diabetes mellitus, porphyria, hypothyroidism or fever 2) increased toxicity in patients with nephrotic syndrome 3) may increase frequency of petit mal seizures Dosage: 1) load 15-30 mg/kg up to 1000 mg IV/IM 2) infusion rate at 100-150 mg/min 3) prescribe & dispense in phenytoin equivalents Injection: 1) 150 mg (equivalent to 100 mg phenytoin) in 2 mL vials 2) 750 mg (equivalent to 500 mg phenytoin) in 10 mL vials Pharmacokinetics: 1) following parenteral administration, fosphenytoin is converted to phenytoin 2) for every mmol of fosphenytoin, 1 mmol of phenytoin is produced 3) the pharmacologic effects of fosphenytoin include those of phenytoin 4) fosphenytoin hydrolysis also results in formaldehyde & phosphate 5) formaldehyde is subsequently converted to formate which is metabolized via folate-dependent mechanisms 6) although formaldehyde has toxic effects, these occur at concentrations in excess of those produced by therapeutic fosphenytoin administration 7) 100% bioavailability via IM or IV route Monitor: 1) blood pressure 2) vital signs 3) complete blood count 4) liver function tests 5) free phenytoin levels inpatients with hepatic or renal insufficiency Adverse effects: 1) not common (1-10%) - facial edema, slurred speech, dizziness, drowsiness, choreoathetosis, fever, visual hallucinations, rash, exfoliative dermatitis, erythema multiforme, acne, folic acid depletion, osteomalacia, gynecomastia, nausea/vomiting, gingival hyperplasia, priapism, lymphadenopathy, neutropenia, thrombocytopenia, megaloblastic anemia, nystagmus, blurred vision, diplopia, nephrotic syndrome 2) other - irritation & necrosis at site of injection is reduced relative to phenytoin - perineal pruritus - increased risk of Stevens Johnson syndrome & toxic epidermal necrolysis in Asian patients positive for HLA allele, HLA-B*1502 [5] Test interactions: 1) increases serum glucose & alkaline phosphatase 2) decreases serum thyroxine, Ca+2, testosterone 3) serum Na+ increases with overdose Laboratory: - fosphenytoin in serum/plasma

Interactions

drug interactions drug adverse effects of anticonvulsants monitor with anticonvulsants

Related

phenytoin; diphenylhydantoin; PTN (Dilantin, Dephenylan, Antilepsin)

General

anticonvulsant hydantoin; glycolylurea

Properties

SIZE: MW = 406 G/M MISC-INFO: elimination route LIVER

Database Correlations

PUBCHEM correlations

References

  1. PDR 1997
  2. Alan Gelb, UCSF, Department of Emergency Services, San Francisco General Hospital, 1998
  3. Drug Information & Medication Formulary, Veterans Affairs, Central California Health Care System, 1st ed., Ravnan et al eds, 1998
  4. Kaiser Permanente Northern California Regional Drug Formulary, 1998
  5. FDA MedWatch http://www.fda.gov/medwatch/safety/2008/safety08.htm#Phenytoin
  6. Deprecated Reference