What it's used for
Fosphenytoin sodium injection is used for the treatment of generalized tonic-clonic status epilepticus and the prevention and treatment of seizures during neurosurgery. It can also be used as a short-term substitute when oral phenytoin is not possible.
Source: U.S. FDA-approved prescribing information (openFDA).
Typical dosing
The adult loading dose for status epilepticus is 15 to 20 mg PE/kg administered at a rate of 100 to 150 mg PE/min.
Dosing shown here is the general FDA-labeled range. Your prescribing clinician determines the exact dose, form, and schedule for you — this is not a substitute for medical advice.
Boxed warning / key safety info
Intravenous administration should not exceed 150 mg PE per minute in adults due to the risk of severe low blood pressure and heart rhythm abnormalities.
Common side effects
Serious adverse reactions include cardiovascular risks from rapid infusion, seizures, serious skin reactions, and hypersensitivity.
Covered strengths on the Tab $0 list
Covered at $0 with an active Tab membership when filled at a participating pharmacy nationwide or through mail order. A licensed clinician must prescribe the medication.
Related medications
Other everything else medications covered at $0 with an active Tab membership.
Fosphenytoin dosage and administration
The dose, concentration, and infusion rate of fosphenytoin sodium injection should always be expressed as phenytoin sodium equivalents (PE) ( 2.1 ) For Status Epilepticus: Adult loading dose is 15 to 20 mg PE/kg at a rate of 100 to 150 mg PE/min ( 2.3 ) Pediatric loading dose is 15 to 20 mg PE/kg at a rate of 2 mg PE/kg/min (or 150 mg PE/min, whichever is slower) ( 2.3 ) For Non-emergent Loading and Maintenance Dosing: Adult loading dose is 10 to 20 mg PE/kg given IV or IM; initial maintenance dose is 4 to 6 mg PE/kg/day in divided doses ( 2.4 ) Pediatric loading dose is 10 to 15 mg PE/kg at a rate of 1 to 2 mg PE/kg/min (or 150 mg PE/min, whichever is slower);
Excerpt from the FDA-approved prescribing information (openFDA), retrieved 2026-09-15. Your prescribing clinician decides the exact dose, form and schedule for you — this is not medical advice.
Fosphenytoin side effects
The following serious adverse reactions are described elsewhere in the labeling: Cardiovascular Risk Associated with Rapid Infusion [see Warnings and Precautions (5.2) ] Withdrawal Precipitated Seizure, Status Epilepticus [see Warnings and Precautions (5.3) ] Serious Dermatologic Reactions [see Warnings and Precautions (5.4) ] Drug Reaction with Eosinophilia and Systemic Symptoms (DRESS)/Multiorgan Hypersensitivity [see Warnings and Precautions (5.5) ] Hypersensitivity [see Warnings and Precautions (5.6) ] Angioedema [see Warnings and Precautions (5.7) ] Hepatic Injury [see Warnings and Precautions (5.8) ] Hematopoietic Complications [see Warnings and Precautions (5.9) ] Sensory Disturbances [see Warnings and Precautions (5.10) ] Local Toxicity (Including Purple Glove Syndrome) [see Warnings and Precautions (5.11) ] Exacerbation of Porphyria [see Warnings and Precautions (5.14) ] Teratogenicity and Other Harm to the Newborn [see Warnings and Precautions (5.15) ] Hyperglycemia [see Warnings and Precautions (5.16) ] Most common adverse reactions (incidence ≥10%) are: • Adults: pruritus, nystagmus, dizziness, somnolence, and ataxia • Pediatrics: vomiting, nystagmus, and ataxia ( 6.1 ) To report SUSPECTED ADVERSE REACTIONS, contact Gland Pharma Limited at 864-879-9994 or FDA at 1-800-FDA-1088 or www.fda.gov/medwatch .
Excerpt from the FDA-approved prescribing information (openFDA), retrieved 2026-09-15. This is not a complete list. Report side effects to your clinician, and seek care for anything severe or unexpected.
Fosphenytoin drug interactions
Fosphenytoin is extensively bound to human plasma proteins. Drugs highly bound to albumin could increase the unbound fraction of fosphenytoin. Although, it is unknown whether this could result in clinically significant effects, caution is advised when administering fosphenytoin sodium with other drugs that significantly bind to serum albumin. The most significant drug interactions following administration of fosphenytoin sodium are expected to occur with drugs that interact with phenytoin. Phenytoin is extensively bound to serum plasma proteins and is prone to competitive displacement. Phenytoin is primarily metabolized by the hepatic cytochrome P450 enzyme CYP2C9 and to a lesser extent by CYP2C19 and is particularly susceptible to inhibitory drug interactions because it is subject to saturable metabolism.
Excerpt from the FDA-approved prescribing information (openFDA), retrieved 2026-09-15. Tell your clinician and pharmacist about every medication, supplement and over-the-counter product you take.
Who should not take fosphenytoin
Fosphenytoin sodium is contraindicated in patients with: A history of hypersensitivity to fosphenytoin sodium injection or its inactive ingredients, or to phenytoin or other hydantoins [see Warnings and Precautions (5.6) ] . Reactions have included angioedema. Sinus bradycardia, sino-atrial block, second and third degree A-V block, or Adams-Stokes syndrome because of the effect of parenteral phenytoin or fosphenytoin sodium on ventricular automaticity. A history of prior acute hepatotoxicity attributable to fosphenytoin sodium or phenytoin [see Warnings and Precautions (5.8) ] . Coadministration with delavirdine because of the potential for loss of virologic response and possible resistance to delavirdine or to the class of non-nucleoside reverse transcriptase inhibitors.
Excerpt from the FDA-approved prescribing information (openFDA), retrieved 2026-09-15. Whether this medication is appropriate for you is a clinical decision made by your prescribing clinician.
Common questions
Is fosphenytoin covered at $0 with Tab?
Yes. Fosphenytoin is on Tab's covered $0 generic list — every covered strength is $0 with an active membership, at participating pharmacies nationwide or by mail order.
Do I need insurance to get fosphenytoin through Tab?
No. Tab is a membership, not insurance. Covered medications are $0 with an active membership whether or not you have a health plan.
How do I get a fosphenytoin prescription with Tab?
Book a video visit with a licensed Tab clinician (unlimited visits are included with membership). If it's clinically appropriate, they send the prescription to your chosen participating pharmacy or by mail order.
What is the usual dose of fosphenytoin?
The dose, concentration, and infusion rate of fosphenytoin sodium injection should always be expressed as phenytoin sodium equivalents (PE) ( 2.1 ) For Status Epilepticus: Adult loading dose is 15 to 20 mg PE/kg at a rate of 100 to 150 mg PE/min ( 2.3 ) Pediatric loading dose is 15 to 20 mg PE/kg at a rate of 2 mg PE/kg/min (or 150 mg PE/min, whichever is slower) ( 2.3 ) For Non-emergent Loading and Maintenance Dosing: Adult loading dose is 10 to 20 mg PE/kg given IV or IM; (FDA-approved label, retrieved 2026-09-15. Your clinician sets your dose.)
What are the side effects of fosphenytoin?
The following serious adverse reactions are described elsewhere in the labeling: Cardiovascular Risk Associated with Rapid Infusion [see Warnings and Precautions (5.2) ] Withdrawal Precipitated Seizure, Status Epilepticus [see Warnings and Precautions (5.3) ] Serious Dermatologic Reactions [see Warnings and Precautions (5.4) ] Drug Reaction with Eosinophilia and Systemic Symptoms (DRESS)/Multiorgan Hypersensitivity [see Warnings and Precautions (5.5) ] Hypersensitivity [see Warnings and Precautions (5.6) ] Angioedema [see Warnings and Precautions (5.7) ] Hepatic Injury [see Warnings and Precautions (5.8) ] Hematopoietic Complications [see Warnings and Precautions (5.9) ] Sensory Disturbances [see Warnings and Precautions (5.10) ] Local Toxicity (Including Purple Glove Syndrome) [see Warnings and Precautions (5.11) ] Exacerbation of Porphyria [see Warnings and Precautions (5.14) ] Teratogenicity and Other Harm to the Newborn [see Warnings and Precautions (5.15) ] Hyperglycemia [see Warnings and Precautions (5.16) ] Most common adverse reactions (incidence ≥10%) are: • Adults: pruritus, nystagmus, dizziness, somnolence, and ataxia • Pediatrics: vomiting, nystagmus, and ataxia ( 6.1 ) To report SUSPECTED ADVERSE REACTIONS, contact Gland Pharma Limited at 864-879-9994 or FDA at 1-800-FDA-1088 or www.fda.gov/medwatch . (FDA-approved label, retrieved 2026-09-15.)
What interacts with fosphenytoin?
Fosphenytoin is extensively bound to human plasma proteins. Drugs highly bound to albumin could increase the unbound fraction of fosphenytoin. Although, it is unknown whether this could result in clinically significant effects, caution is advised when administering fosphenytoin sodium with other drugs that significantly bind to serum albumin. (FDA-approved label, retrieved 2026-09-15. Tell your clinician about every medication and supplement you take.)
Fosphenytoin is $0 on the covered list
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