Fosphenytoin Brand Name– Cerebyx
What is Fosphenytoin
Fosphenytoin is a water-soluble, parenteral prodrug of phenytoin. Intravenous (IV) or intramuscular (IM) fosphenytoin may be substituted short-term for oral phenytoin in situations where oral phenytoin is not appropriate or advantageous.
Unlike phenytoin, fosphenytoin is soluble in standard intravenous solutions and is rapidly absorbed via the IM route.
Fosphenytoin has fewer local adverse effects and does not contain propylene glycol; thus, IV doses can be given at a faster rate. Since fosphenytoin is converted to phenytoin in vivo, systemic adverse effects are generally similar between the two products.
While fosphenytoin represents an improvement over phenytoin in terms of infusion-related reactions, fosphenytoin causes transient, infusion-related, paresthesias and pruritus not seen with phenytoin.
These effects disappear upon stopping or lowering the rate of infusion.
Fosphenytoin is more expensive than corresponding doses of generic phenytoin but is an attractive alternative when IV access is limited or tenuous.
Fosphenytoin was approved by the FDA in August 1996 for patients 18 years and older.
Approval was expanded to include pediatric patients from neonates to 17 years of age in March 2017
Indications
- partial seizures
- seizure prophylaxis
- status epilepticus
- tonic-clonic seizures
NOTE: The dose, concentration, and infusion rate for fosphenytoin should always be prescribed and dispensed as phenytoin equivalents (PE). Fosphenytoin’s dose is expressed as PE to avoid the need to perform molecular weight-based adjustments when converting between fosphenytoin and phenytoin doses
Side Effects
- acute generalized exanthematous pustulosis (AGEP)
- agitation
- agranulocytosis
- akathisia
- amblyopia
- amnesia
- anaphylactoid reactions
- anemia
- angioedema
- anorexia
- aphasia
- apnea
- arthralgia
- asthenia
- ataxia
- atrial flutter
- back pain
- bradycardia
- bronchospasm
- bullous rash
- bundle-branch block
- cardiac arrest
- cerebral edema
- chills
- coma
- confusion
- conjunctivitis
- constipation
- contact dermatitis
- cough
- cyanosis
- dehydration
- depression
- diabetes insipidus
- diarrhea
- diplopia
- dizziness
- drowsiness
- Drug Reaction with Eosinophilia and Systemic Symptoms (DRESS)
- dysarthria
- dysgeusia
- dyspepsia
- dysphagia
- dyspnea
- dysuria
- ecchymosis
- edema
- elevated hepatic enzymes
- emotional lability
- encephalopathy
- eosinophilia
- epistaxis
- erythema multiforme
- exfoliative dermatitis
- fever
- flatulence
- folate deficiency
- gastritis
- GI bleeding
- gingival hyperplasia
- headache
- hearing loss
- heart failure
- hemoptysis
- hepatic failure
- hepatomegaly
- hirsutism
- hostility
- hyperacusis
- hyperesthesia
- hyperglycemia
- hyperhidrosis
- hyperkalemia
- hyperkinesis
- hyperphosphatemia
- hyperreflexia
- hypersalivation
- hypertension
- hypertrichosis
- hyperventilation
- hypoesthesia
- hypokalemia
- hypophosphatemia
- hyporeflexia
- hypotension
- hypotonia
- hypoxia
- ileus
- infection
- infusion-related reactions
- injection site reaction
- insomnia
- jaundice
- leukocytosis
- leukopenia
- lupus-like symptoms
- lymphadenopathy
- maculopapular rash
- malaise
- meningitis
- migraine
- muscle cramps
- myalgia
- myasthenia
- mydriasis
- myoclonia
- myopathy
- nausea
- neutropenia
- nystagmus
- ocular pain
- oliguria
- orthostatic hypotension
- osteomalacia
- otalgia
- palpitations
- pancytopenia
- paresthesias
- parosmia
- pelvic pain
- peripheral vasodilation
- petechiae
- pharyngitis
- photophobia
- photosensitivity
- pneumothorax
- polyuria
- proteinuria
- pruritus
- psychosis
- pulmonary embolism
- purpura
- QT prolongation
- rash
- renal failure (unspecified)
- rhinitis
- seizures
- sinus tachycardia
- sinusitis
- skin discoloration
- skin necrosis
- Stevens-Johnson syndrome
- stroke
- subdural hematoma
- suicidal ideation
- syncope
- tenesmus
- teratogenesis
- thrombocytopenia
- tinnitus
- toxic epidermal necrolysis
- tremor
- urethral pain
- urinary incontinence
- urinary retention
- urticaria
- vaginitis
- ventricular fibrillation
- vertigo
- visual impairment
- vitamin D deficiency
- vomiting
- xerostomia
Monitoring Parameters
- CBC
- LFTs
- neurologic function
- serum albumin
- serum phenytoin concentrations
Contraindications
- abrupt discontinuation
- Adams-Stokes syndrome
- agranulocytosis
- alcoholism
- Asian patients
- AV block
- barbiturate hypersensitivity
- bone marrow suppression
- bradycardia
- breast-feeding
- bundle-branch block
- carbamazepine hypersensitivity
- cardiac arrhythmias
- cardiac disease
- contraception requirements
- dental disease
- dental work
- depression
- diabetes mellitus
- driving or operating machinery
- encephalopathy
- geriatric
- hematological disease
- hemolytic anemia
- hepatic disease
- hepatotoxicity
- Hodgkin lymphoma
- hydantoin hypersensitivity
- hypoalbuminemia
- hypoglycemia
- hyponatremia
- hypotension
- hypothyroidism
- infusion-related reactions
- intravenous administration
- jaundice
- leukopenia
- lymphoma
- methemoglobin reductase deficiency
- methemoglobinemia
- myasthenia gravis
- neonates
- neutropenia
- obstetric delivery
- osteomalacia
- osteoporosis
- petit mal (absence) seizures
- porphyria
- pregnancy
- psychosis
- radiation therapy
- renal disease
- renal failure
- renal impairment
- reproductive risk
- succinimide hypersensitivity
- suicidal ideation
- thrombocytopenia
- thyroid disease
- vitamin K deficiency
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- Sitagliptin
- Sofosbuvir
- Sofosbuvir; Velpatasvir
- Sofosbuvir; Velpatasvir; Voxilaprevir
- Sonidegib
- Sorafenib
- St. John’s Wort, Hypericum perforatum
- Streptozocin
- Succinylcholine
- Sufentanil
- Sulfamethoxazole; Trimethoprim, SMX-TMP, Cotrimoxazole
- Sulfinpyrazone
- Sulfonylureas
- Sunitinib
- Suvorexant
- Tacrolimus
- Tadalafil
- Tamoxifen
- Tasimelteon
- Tazemetostat
- Telithromycin
- Telotristat Ethyl
- Temazepam
- Temsirolimus
- Teniposide
- Tenofovir Alafenamide
- Terbinafine
- Tetracaine
- Tezacaftor; Ivacaftor
- Thalidomide
- Theophylline, Aminophylline
- Thiazolidinediones
- Thiopental
- Thiotepa
- Thiothixene
- Thyroid hormones
- Tiagabine
- Ticagrelor
- Ticlopidine
- Tinidazole
- Tipranavir
- Tizanidine
- Tocilizumab
- Tofacitinib
- Tolvaptan
- Topiramate
- Toremifene
- Trabectedin
- Tramadol
- Trandolapril; Verapamil
- Tranylcypromine
- Trazodone
- Tretinoin, ATRA
- Triamcinolone
- Triazolam
- Triclabendazole
- Tricyclic antidepressants
- Trimethoprim
- Trimetrexate
- Trimipramine
- Triprolidine
- Tubocurarine
- Tucatinib
- Ubrogepant
- Ulipristal
- Upadacitinib
- Valacyclovir
- Valbenazine
- Valdecoxib
- Valproic Acid, Divalproex Sodium
- Vandetanib
- Vecuronium
- Vemurafenib
- Venetoclax
- Verapamil
- Vigabatrin
- Vilazodone
- Vincristine
- Vincristine Liposomal
- Vorapaxar
- Voriconazole
- Vortioxetine
- Voxelotor
- Warfarin
- Zafirlukast
- Zalcitabine, ddC
- Zaleplon
- Zanubrutinib
- Zidovudine, ZDV
- Ziprasidone
- Zolpidem
- Zonisamide
