Fosphenytoin Eugia: Uses, Dosage & Side Effects
A water-soluble prodrug of phenytoin for the treatment of status epilepticus and the prevention of seizures during neurosurgery, administered intravenously or intramuscularly
Fosphenytoin Eugia is a prescription injectable antiepileptic medication containing fosphenytoin sodium, a water-soluble phosphate ester prodrug of phenytoin. It is used in hospital settings for the treatment of generalized tonic-clonic status epilepticus, the prevention and treatment of seizures occurring during or following neurosurgery or head trauma, and as a short-term parenteral substitute for oral phenytoin when oral administration is temporarily not feasible. After intravenous or intramuscular administration, fosphenytoin is rapidly and completely converted to phenytoin, which stabilizes neuronal membranes by modulating voltage-gated sodium channels. Fosphenytoin offers significant advantages over intravenous phenytoin, including a faster infusion rate, lower risk of injection site reactions, the option of intramuscular administration, and improved tolerability. All doses are expressed in phenytoin equivalents (PE) to facilitate safe dosing conversions.
Quick Facts: Fosphenytoin Eugia
Key Takeaways
- Fosphenytoin Eugia is a water-soluble prodrug of phenytoin used primarily for the treatment of status epilepticus and perioperative seizure prevention, offering a safer parenteral alternative to intravenous phenytoin with reduced risk of tissue damage and cardiovascular complications.
- Doses are expressed in phenytoin equivalents (PE), where 1.5 mg of fosphenytoin sodium equals 1 mg PE, ensuring safe and accurate conversion between fosphenytoin and oral or intravenous phenytoin.
- Fosphenytoin can be administered intravenously at up to 150 mg PE/min (compared to only 50 mg/min for phenytoin) and can also be given intramuscularly, providing greater dosing flexibility in emergency and perioperative settings.
- Continuous cardiac monitoring (ECG), blood pressure monitoring, and respiratory monitoring are mandatory during and for at least 30 minutes after intravenous infusion due to the risk of hypotension, bradycardia, and cardiac arrhythmias.
- Phenytoin, the active metabolite, has a narrow therapeutic index with target plasma levels of 10–20 mg/L and exhibits nonlinear pharmacokinetics, requiring careful dose adjustment and therapeutic drug monitoring to avoid toxicity.
What Is Fosphenytoin Eugia and What Is It Used For?
Fosphenytoin Eugia contains fosphenytoin sodium, which is a disodium phosphate ester prodrug of phenytoin. Phenytoin has been one of the most widely used antiepileptic drugs since its introduction in 1938, and it remains a first-line treatment for the management of status epilepticus and a cornerstone of seizure prophylaxis in neurosurgical and neurocritical care settings. However, intravenous phenytoin has long been associated with significant limitations, including a highly alkaline pH (approximately 12) that causes local tissue injury and phlebitis, a maximum safe infusion rate of only 50 mg/min, incompatibility with dextrose-containing solutions, the risk of purple glove syndrome, and the impossibility of intramuscular administration due to erratic absorption and tissue necrosis.
Fosphenytoin was developed specifically to address these limitations. As a water-soluble prodrug with a near-physiological pH of 8.6 to 9.0, fosphenytoin can be administered much more safely via both the intravenous and intramuscular routes. After parenteral administration, fosphenytoin is rapidly and completely converted to phenytoin by ubiquitous phosphatases in the blood and tissues, with a conversion half-life of approximately 15 minutes. This means that the pharmacological activity of fosphenytoin is entirely attributable to phenytoin, and the clinical efficacy and therapeutic monitoring are identical to those of phenytoin itself.
Phenytoin exerts its antiepileptic effect through modulation of voltage-gated sodium channels in neuronal membranes. At therapeutic concentrations, phenytoin selectively blocks the sustained, high-frequency repetitive firing of action potentials that occurs during seizure activity, while having minimal effect on normal neuronal firing. This is achieved through use-dependent blockade of sodium channels: phenytoin binds preferentially to the inactivated state of the sodium channel, stabilizing it and preventing its return to the active, resting state. This mechanism limits the spread of seizure activity in the cerebral cortex without significantly depressing normal brain function. Additionally, phenytoin has effects on calcium and potassium channels that contribute to its ability to stabilize excitable membranes.
Approved Indications
Fosphenytoin Eugia is approved for the following clinical indications:
- Status epilepticus: Generalized tonic-clonic status epilepticus (GCSE) is a life-threatening neurological emergency defined as continuous seizure activity lasting more than 5 minutes, or two or more seizures without full recovery of consciousness between episodes. Fosphenytoin is used as a second-line agent after benzodiazepines (such as lorazepam or diazepam) have been administered. International guidelines from the International League Against Epilepsy (ILAE), the Neurocritical Care Society (NCS), and the American Epilepsy Society (AES) all include fosphenytoin (or phenytoin) as a recommended second-line treatment for established status epilepticus.
- Prevention and treatment of seizures during neurosurgery: Patients undergoing craniotomy, tumor resection, or other intracranial procedures are at significant risk of perioperative seizures. Fosphenytoin is administered prophylactically before, during, or after neurosurgery to reduce this risk. It is also used for seizure prophylaxis following traumatic brain injury, particularly in the acute phase (first 7 days), as supported by evidence from the landmark study by Temkin et al. and subsequent guidelines.
- Short-term parenteral substitution for oral phenytoin: When patients who are maintained on oral phenytoin are temporarily unable to take oral medication (due to surgery, gastrointestinal conditions, altered consciousness, or other clinical situations), fosphenytoin provides a reliable parenteral alternative. The intramuscular route is particularly valuable in situations where intravenous access is difficult to establish or maintain.
It is important to understand that fosphenytoin is not used for the acute termination of individual seizures (that role belongs to benzodiazepines) but rather for the establishment and maintenance of therapeutic phenytoin levels in patients who require rapid parenteral anticonvulsant therapy. In the stepped management of status epilepticus, fosphenytoin is typically administered after initial benzodiazepine therapy has failed to terminate seizure activity.
All fosphenytoin doses are expressed in phenytoin equivalents (PE) to simplify dosing and prevent errors. One milligram PE of fosphenytoin delivers the equivalent of one milligram of phenytoin sodium. Fosphenytoin Eugia contains 75 mg/mL of fosphenytoin sodium, which is equivalent to 50 mg PE/mL. This standardized convention is critical for patient safety, as it allows direct substitution between fosphenytoin and phenytoin without the need for complex dose calculations.
What Should You Know Before Taking Fosphenytoin Eugia?
Contraindications
Fosphenytoin Eugia is contraindicated in the following clinical situations, and it must not be administered to patients who meet any of these criteria:
- Hypersensitivity: Known hypersensitivity to fosphenytoin, phenytoin, other hydantoin derivatives (such as ethotoin), or to any of the excipients in the formulation. Severe allergic reactions, including anaphylaxis, angioedema, and Stevens-Johnson syndrome (SJS)/toxic epidermal necrolysis (TEN), have been reported with phenytoin and fosphenytoin.
- Cardiac conduction disorders: Sinus bradycardia, sinoatrial block, second-degree atrioventricular (AV) block, third-degree AV block (complete heart block), and Adams-Stokes syndrome. Phenytoin has direct effects on the cardiac conduction system and can exacerbate these conditions, potentially leading to cardiac arrest.
- Concurrent use with delavirdine: Co-administration with delavirdine (an HIV non-nucleoside reverse transcriptase inhibitor) is contraindicated because phenytoin significantly reduces delavirdine plasma concentrations, potentially leading to loss of virologic response and possible resistance to delavirdine or to the class of NNRTIs.
Warnings and Precautions
Rapid intravenous administration of fosphenytoin can cause severe hypotension, bradycardia, cardiac arrhythmias, and cardiac arrest. The infusion rate must not exceed 150 mg PE/min in adults and 2 mg PE/kg/min (or 150 mg PE/min, whichever is slower) in pediatric patients. Continuous ECG monitoring, blood pressure monitoring, and respiratory monitoring are mandatory during infusion and for at least 30 minutes after completion. Resuscitation equipment must be immediately available.
Before initiating fosphenytoin therapy, clinicians must be aware of the following important safety considerations:
- Cardiovascular monitoring: Phenytoin has direct depressant effects on the cardiac conduction system, primarily by prolonging the effective refractory period and slowing conduction in the bundle of His and Purkinje fibers. These effects are dose- and rate-dependent. Severe cardiovascular events, including fatal cardiac arrest, have occurred during and shortly after intravenous fosphenytoin/phenytoin infusion, particularly when the recommended infusion rate was exceeded. Elderly patients and those with pre-existing cardiovascular disease are at highest risk.
- Severe cutaneous adverse reactions (SCARs): Phenytoin has been associated with potentially life-threatening skin reactions, including Stevens-Johnson syndrome (SJS), toxic epidermal necrolysis (TEN), and drug reaction with eosinophilia and systemic symptoms (DRESS). These reactions typically occur within the first 2–8 weeks of treatment. Patients of Southeast Asian ancestry who carry the HLA-B*1502 allele are at significantly increased risk of SJS/TEN with phenytoin. Where feasible, HLA-B*1502 testing should be performed before initiating phenytoin therapy in patients of at-risk ethnic backgrounds. If any signs of skin rash develop, fosphenytoin must be discontinued immediately.
- Purple glove syndrome: Although less common with fosphenytoin than with phenytoin, purple glove syndrome (characterized by edema, discoloration, and pain distal to the injection site) can still occur with intravenous fosphenytoin. The injection site should be monitored for signs of local irritation during and after administration.
- Hepatotoxicity: Phenytoin is metabolized by the liver, primarily by CYP2C9 and CYP2C19 enzymes. Cases of acute hepatotoxicity, including hepatic failure and death, have been reported. Patients with hepatic impairment may have increased unbound phenytoin fractions and require dose adjustment.
- Hematologic effects: Phenytoin can cause hematologic complications including megaloblastic anemia (due to folate depletion), agranulocytosis, granulocytopenia, leukopenia, thrombocytopenia, and pancytopenia. Some cases have been fatal. Complete blood counts should be monitored during prolonged therapy.
- Hyperglycemia: Phenytoin can inhibit insulin release and cause hyperglycemia, particularly in patients with diabetes mellitus. Blood glucose levels should be monitored in diabetic patients.
Pregnancy and Breastfeeding
Phenytoin is classified as a known teratogen based on extensive human and animal data. The use of phenytoin (and therefore fosphenytoin) during pregnancy is associated with a 2–3 fold increased risk of major congenital malformations compared with the general population. The characteristic pattern of abnormalities associated with prenatal phenytoin exposure is known as fetal hydantoin syndrome, which includes craniofacial dysmorphism (wide nasal bridge, short nose, hypertelorism), distal digital hypoplasia (small or absent fingernails and toenails), growth restriction, and developmental delay. Cleft lip and palate, cardiac defects (particularly ventricular septal defects), and urogenital malformations have also been reported at increased frequency.
Despite these risks, uncontrolled seizures during pregnancy also pose serious dangers to both the mother and fetus, including hypoxia, trauma, and fetal death. Therefore, the decision to use fosphenytoin during pregnancy must be made on an individual basis, weighing the potential benefit of seizure control against the known teratogenic risks. Women of childbearing potential should be counseled about the risks before treatment, and effective contraception should be used. Phenytoin reduces the efficacy of hormonal contraceptives, so additional or alternative contraceptive methods may be required. Folic acid supplementation (at a dose of 5 mg daily) is recommended for all women of childbearing potential taking phenytoin, as phenytoin depletes folate stores and folate deficiency is independently associated with neural tube defects.
Phenytoin is excreted in breast milk in small amounts. The estimated infant exposure through breast milk is approximately 5% of the maternal weight-adjusted dose. Although the amount transferred is generally considered compatible with breastfeeding, neonates should be monitored for signs of sedation, poor feeding, or other adverse effects. The benefits of breastfeeding should be weighed against the potential risk to the infant.
How Does Fosphenytoin Eugia Interact with Other Drugs?
Phenytoin is one of the most extensively interacting drugs in clinical pharmacology. It is primarily metabolized by the hepatic cytochrome P450 enzymes CYP2C9 and CYP2C19, and it is a potent inducer of multiple CYP enzymes, including CYP3A4, CYP2B6, CYP2C9, and CYP2C19, as well as UDP-glucuronosyltransferases (UGTs) and P-glycoprotein. Because of its narrow therapeutic index and nonlinear pharmacokinetics, even small changes in phenytoin metabolism can result in clinically significant alterations in plasma levels, leading to either toxicity or loss of seizure control.
The following table summarizes the most clinically important drug interactions with phenytoin. This is not an exhaustive list, and healthcare professionals should consult comprehensive drug interaction databases when prescribing fosphenytoin alongside other medications.
Major Interactions
| Interacting Drug/Class | Effect | Clinical Significance |
|---|---|---|
| Carbamazepine | Mutual induction; both levels may decrease | Monitor levels of both drugs; dose adjustment often needed |
| Valproic acid | Displaces phenytoin from protein binding; inhibits phenytoin metabolism | Free phenytoin increases; total phenytoin may decrease. Monitor free levels |
| Warfarin | Phenytoin induces warfarin metabolism; complex bidirectional interaction | Reduced anticoagulant effect; monitor INR closely. Increased bleeding risk initially |
| Oral contraceptives | Phenytoin induces metabolism of ethinyl estradiol and progestogens | Contraceptive failure; use additional or alternative contraception |
| Corticosteroids | Phenytoin induces corticosteroid metabolism via CYP3A4 | Reduced corticosteroid efficacy; higher doses may be needed |
| Cyclosporine | Phenytoin induces cyclosporine metabolism | Reduced immunosuppression; monitor cyclosporine levels closely |
| Methotrexate | Phenytoin may reduce methotrexate efficacy; methotrexate may increase free phenytoin | Monitor efficacy and phenytoin levels during co-administration |
| Fluconazole / Voriconazole | Strong CYP2C9 inhibitors; significantly increase phenytoin levels | Risk of phenytoin toxicity; reduce phenytoin dose and monitor levels |
Minor Interactions
In addition to the major interactions listed above, phenytoin interacts with a broad range of other medications through its enzyme-inducing properties. Drugs whose efficacy may be reduced by concurrent phenytoin use include (but are not limited to): calcium channel blockers (particularly nifedipine and felodipine), statins (atorvastatin, simvastatin), antifungals (itraconazole, posaconazole), antiretrovirals (many protease inhibitors and NNRTIs), certain antibiotics (doxycycline), vitamin D and calcium metabolism, thyroid hormones, and many chemotherapy agents.
Conversely, several drugs can increase phenytoin plasma levels by inhibiting its metabolism, including amiodarone, chloramphenicol, cimetidine, fluoxetine, isoniazid, omeprazole, and trimethoprim. Other drugs can decrease phenytoin levels through enzyme induction or reduced absorption, including rifampin, chronic alcohol use, carbamazepine, and sucralfate. Enteral nutrition (tube feeding) can significantly reduce phenytoin absorption, and feeding should be held for 1–2 hours before and after phenytoin administration.
Due to the narrow therapeutic index and extensive drug interactions of phenytoin, therapeutic drug monitoring (TDM) is essential whenever fosphenytoin/phenytoin is used concurrently with other medications. The target total phenytoin plasma concentration is 10–20 mg/L (40–80 micromol/L), and free (unbound) phenytoin levels of 1–2 mg/L should be used in patients with hypoalbuminemia, renal impairment, or when protein-binding interactions are suspected.
What Is the Correct Dosage of Fosphenytoin Eugia?
All fosphenytoin doses are expressed in milligrams of phenytoin equivalents (mg PE). Fosphenytoin Eugia contains 75 mg/mL of fosphenytoin sodium, equivalent to 50 mg PE/mL. Fosphenytoin can be diluted in 5% dextrose or 0.9% sodium chloride solutions to a concentration of 1.5–25 mg PE/mL. The route of administration, infusion rate, and dose depend on the clinical indication.
Adults
Status Epilepticus (Loading Dose)
Loading dose: 20 mg PE/kg administered intravenously at a rate of 100–150 mg PE/min. If seizures are not controlled, additional doses of 5 mg PE/kg may be considered. In elderly patients or those with cardiovascular disease, the infusion rate should be reduced to 50–100 mg PE/min. The loading dose should be followed by appropriate maintenance therapy.
Non-Emergency Loading Dose (Seizure Prophylaxis)
Loading dose: 10–15 mg PE/kg administered intravenously at 50–100 mg PE/min, or intramuscularly. For neurosurgical prophylaxis, the loading dose is typically administered before or during surgery. The intramuscular route can be used when IV access is not available; IM fosphenytoin is well absorbed and provides reliable phenytoin plasma levels.
Maintenance Dose
Maintenance dose: 4–5 mg PE/kg/day administered intravenously (at a rate of 50–100 mg PE/min) or intramuscularly, divided into 1–2 doses per day. Maintenance dosing should begin 12 hours after the loading dose. Transition to oral phenytoin should occur as soon as clinically feasible. Therapeutic drug monitoring is essential to guide maintenance dosing.
Children and Adolescents
Fosphenytoin is used in pediatric patients for the same indications as in adults, although specific pediatric dosing data for fosphenytoin are more limited. The following doses are based on available evidence and clinical practice guidelines:
Pediatric Status Epilepticus Loading Dose
Loading dose: 20 mg PE/kg administered intravenously at a maximum rate of 2 mg PE/kg/min (not exceeding 150 mg PE/min). Neonates may require lower infusion rates. Children generally have faster phenytoin clearance than adults and may require relatively higher weight-based maintenance doses.
Pediatric Maintenance Dose
Maintenance dose: 5–8 mg PE/kg/day, divided into 2 doses. Children aged 6 months to 6 years typically require higher weight-based doses (8–10 mg PE/kg/day) due to faster hepatic metabolism. Therapeutic drug monitoring is particularly important in pediatric patients due to age-related pharmacokinetic variability.
Elderly Patients
Elderly patients are at increased risk of cardiovascular complications during fosphenytoin infusion, including hypotension, bradycardia, and cardiac arrhythmias. The infusion rate should be reduced in elderly patients, typically not exceeding 50–100 mg PE/min for loading doses. Elderly patients also frequently have lower albumin levels and reduced hepatic function, leading to higher free phenytoin fractions and an increased risk of toxicity at apparently normal total phenytoin plasma concentrations. Free phenytoin level monitoring is recommended in elderly patients. Maintenance doses may need to be lower (3–4 mg PE/kg/day) due to reduced clearance.
Missed Dose
In the hospital setting where fosphenytoin is administered, missed doses should be avoided as this can lead to subtherapeutic phenytoin levels and breakthrough seizures. If a maintenance dose is missed, it should be given as soon as possible and the regular dosing schedule resumed. The dose should not be doubled to compensate for a missed dose. In patients transitioning from intravenous fosphenytoin to oral phenytoin, careful attention must be paid to the timing of the switch to maintain therapeutic plasma levels continuously.
Overdose
Phenytoin overdose manifests with a predictable progression of neurological symptoms related to plasma concentration:
- 20–30 mg/L: Nystagmus (typically the first sign of toxicity), ataxia, slurred speech
- 30–40 mg/L: Marked ataxia, lethargy, confusion, diplopia
- >40 mg/L: Coma, respiratory depression, cardiovascular collapse
There is no specific antidote for phenytoin overdose. Treatment is supportive, including airway management, hemodynamic support, and monitoring in an intensive care setting. Hemodialysis is not effective for phenytoin removal due to its high protein binding (approximately 90%). However, in patients with very high free phenytoin levels (such as those with hypoalbuminemia or renal failure), high-flux hemodialysis may be considered. Activated charcoal may reduce absorption if administered within 1–2 hours of oral phenytoin ingestion, but this is not relevant for intravenous fosphenytoin overdose. The nonlinear pharmacokinetics of phenytoin mean that the elimination half-life may be markedly prolonged in overdose (up to 60 hours or more), requiring extended monitoring.
What Are the Side Effects of Fosphenytoin Eugia?
Like all medicines, fosphenytoin can cause side effects, although not everyone will experience them. The side effects can be broadly categorized into two groups: those related to the fosphenytoin prodrug itself (which occur during or shortly after infusion and resolve quickly) and those related to phenytoin (which depend on plasma phenytoin levels and may persist for the duration of therapy).
Fosphenytoin-specific effects include transient pruritus and paresthesias (tingling, burning, or itching sensations), which are very common during and shortly after intravenous infusion. These sensations are most frequently reported in the groin, head, and extremities and are thought to be caused by the phosphate moiety of fosphenytoin rather than by phenytoin itself. They are typically mild to moderate, dose-rate dependent, and resolve within minutes of slowing or completing the infusion. Reducing the infusion rate can minimize these effects.
Phenytoin-related side effects are well characterized from decades of clinical experience and are largely dose-dependent and related to plasma phenytoin concentrations. The following categorization is based on the frequency of adverse events observed in clinical trials and post-marketing surveillance data.
Very Common
May affect more than 1 in 10 people
- Nystagmus (involuntary rapid eye movements)
- Dizziness and lightheadedness
- Pruritus (itching, often in the groin area during infusion)
- Paresthesias (tingling or burning sensations during infusion)
- Drowsiness and somnolence
- Ataxia (impaired coordination and unsteady gait)
Common
May affect up to 1 in 10 people
- Headache
- Nausea and vomiting
- Hypotension (low blood pressure)
- Tachycardia (fast heart rate)
- Tremor
- Diplopia (double vision)
- Injection site reactions (pain, burning, erythema)
- Taste perversion (dysgeusia)
- Tinnitus (ringing in the ears)
Uncommon
May affect up to 1 in 100 people
- Bradycardia (slow heart rate)
- Cardiac arrhythmias
- Gingival hyperplasia (gum overgrowth, with prolonged phenytoin use)
- Skin rash (maculopapular or morbilliform)
- Confusion and cognitive impairment
- Hyperglycemia
- Megaloblastic anemia (folate deficiency)
- Elevated liver enzymes
Rare
May affect up to 1 in 1,000 people
- Stevens-Johnson syndrome (SJS)
- Toxic epidermal necrolysis (TEN)
- DRESS syndrome (Drug Reaction with Eosinophilia and Systemic Symptoms)
- Hepatotoxicity and hepatic failure
- Agranulocytosis and pancytopenia
- Systemic lupus erythematosus-like syndrome
- Lymphadenopathy (pseudolymphoma)
- Purple glove syndrome
- Peripheral neuropathy (with long-term use)
- Cerebellar atrophy (with chronic elevated phenytoin levels)
Not Known
Frequency cannot be estimated from available data
- Anaphylaxis
- Angioedema
- Osteomalacia and decreased bone mineral density (long-term phenytoin use)
- Vitamin D deficiency
- Coarsening of facial features (long-term use)
It is important to note that many of the serious adverse effects listed above (SJS/TEN, DRESS, hepatotoxicity, blood dyscrasias) are idiosyncratic rather than dose-dependent, meaning they can occur at any plasma phenytoin concentration. Most dose-dependent side effects (nystagmus, ataxia, drowsiness, confusion) are directly correlated with plasma phenytoin levels and are reversible when levels are brought back within the therapeutic range of 10–20 mg/L.
Long-term phenytoin therapy is associated with a number of chronic effects that are not directly relevant to the acute use of fosphenytoin but are important for patients transitioning to oral phenytoin maintenance. These include gingival hyperplasia (affecting 30–50% of patients on chronic therapy), hirsutism, coarsening of facial features, folate deficiency, vitamin D deficiency with osteomalacia, peripheral neuropathy, and cerebellar atrophy. These effects are reasons why phenytoin has been increasingly replaced by newer antiepileptic drugs for long-term maintenance therapy, while remaining a first-line choice for acute seizure management.
Contact your healthcare provider or seek emergency medical attention immediately if you notice: skin rash, blistering, or peeling of the skin; swelling of the face, lips, tongue, or throat; difficulty breathing; fever with swollen glands; yellowing of the skin or eyes (jaundice); unusual bleeding or bruising; or signs of infection (persistent fever, sore throat). These may be signs of serious reactions that require immediate medical intervention.
How Should You Store Fosphenytoin Eugia?
Proper storage of Fosphenytoin Eugia is essential to maintain the stability, safety, and efficacy of the medication. As a parenteral pharmaceutical product, fosphenytoin solution is sensitive to temperature, light, and time after dilution.
- Unopened vials: Store in a refrigerator at 2–8 °C (36–46 °F). Do not freeze. Freezing may cause physical changes to the product that could affect its safety and efficacy. Keep the vials in the outer carton to protect from light.
- Room temperature storage: Unopened vials may be stored at room temperature (up to 25 °C / 77 °F) for a single period of up to 48 hours. Once removed from refrigeration and stored at room temperature, the product should not be returned to the refrigerator.
- After dilution: Once diluted in 5% dextrose or 0.9% sodium chloride, the solution should be used within 4 hours at room temperature (15–25 °C) or within 24 hours if stored in a refrigerator (2–8 °C). From a microbiological safety perspective, the diluted product should ideally be used immediately.
- Inspection before use: Before administration, visually inspect the solution for particulate matter and discoloration. The solution should be clear and colorless to pale yellow. Do not use if the solution is cloudy, contains particles, or if the vial seal is compromised.
- Single use only: Each vial is for single use. Any unused solution remaining in the vial after withdrawal of the required dose must be discarded. Do not use the product after the expiration date printed on the vial label and carton.
- Disposal: Unused product and waste material should be disposed of in accordance with local hospital pharmaceutical waste protocols and applicable regulations.
Fosphenytoin Eugia is supplied as a concentrated solution for injection/infusion in glass vials. The solution contains 75 mg/mL of fosphenytoin sodium (equivalent to 50 mg PE/mL). Vials are available in 2 mL (150 mg fosphenytoin sodium / 100 mg PE) and 10 mL (750 mg fosphenytoin sodium / 500 mg PE) sizes. Not all vial sizes may be available in all countries.
What Does Fosphenytoin Eugia Contain?
Understanding the composition of Fosphenytoin Eugia is important for healthcare professionals preparing and administering the medication, and for identifying potential hypersensitivity risks related to any of the formulation components.
Active Ingredient
The active substance is fosphenytoin sodium, the disodium phosphate ester of 5,5-diphenylhydantoin (phenytoin). Each milliliter of solution contains 75 mg of fosphenytoin sodium, which is equivalent to 50 mg of phenytoin equivalents (PE). Fosphenytoin sodium has a molecular weight of 406.24 g/mol and is freely soluble in water, which is a key advantage over phenytoin itself (which is poorly water-soluble and requires the highly alkaline vehicle propylene glycol/ethanol for parenteral formulation).
Inactive Ingredients (Excipients)
| Ingredient | Role | Notes |
|---|---|---|
| Fosphenytoin sodium | Active substance (prodrug of phenytoin) | 75 mg/mL (50 mg PE/mL) |
| Tromethamine (THAM) | Buffer (pH stabilizer) | Maintains solution pH at 8.6–9.0 |
| Hydrochloric acid | pH adjustment | Used to achieve target pH |
| Sodium hydroxide | pH adjustment | Used to achieve target pH |
| Water for injections | Solvent | To volume |
Key Formulation Advantages
The formulation of fosphenytoin represents a significant pharmaceutical advancement over the traditional intravenous phenytoin formulation. Intravenous phenytoin requires a vehicle of 40% propylene glycol and 10% ethanol at a pH of approximately 12, which is responsible for many of the local and systemic toxicities associated with phenytoin injection (tissue necrosis, purple glove syndrome, phlebitis, and cardiovascular depression). Fosphenytoin, by contrast, is freely water-soluble and is formulated in a simple aqueous buffer at a near-physiological pH (8.6–9.0), eliminating the need for the toxic propylene glycol/ethanol vehicle. This formulation difference is the primary reason why fosphenytoin can be infused faster, given intramuscularly, and is associated with fewer injection site complications than phenytoin.
Compatibility
Fosphenytoin Eugia can be diluted in 5% dextrose solution (D5W) or 0.9% sodium chloride solution (normal saline) to concentrations of 1.5–25 mg PE/mL. This is an important advantage over phenytoin injection, which is incompatible with dextrose-containing solutions and can only be diluted in normal saline. Fosphenytoin should not be mixed with other medications in the same infusion bag or syringe unless compatibility has been specifically established.
Frequently Asked Questions About Fosphenytoin Eugia
Fosphenytoin Eugia is used for three main indications: (1) the treatment of generalized tonic-clonic status epilepticus, a life-threatening condition involving prolonged or repeated seizures; (2) the prevention and treatment of seizures during or after neurosurgery or head trauma; and (3) as a short-term parenteral substitute for oral phenytoin when patients are temporarily unable to take medication by mouth. It is a hospital-use medication administered by healthcare professionals via intravenous infusion or intramuscular injection.
Fosphenytoin is a water-soluble prodrug that is converted to phenytoin in the body. The key advantages over intravenous phenytoin include: a more neutral pH (8.6–9.0 versus pH 12 for phenytoin), elimination of the toxic propylene glycol/ethanol vehicle, a faster maximum infusion rate (150 mg PE/min versus 50 mg/min), the ability to be given intramuscularly, compatibility with dextrose IV solutions, and a lower risk of injection site complications including purple glove syndrome. The clinical efficacy is identical because the therapeutic effect comes entirely from the phenytoin produced after conversion.
PE stands for Phenytoin Equivalents. Because fosphenytoin is a prodrug that is converted to phenytoin, all doses are expressed in PE to prevent dosing errors and allow direct comparison with phenytoin doses. One milligram PE of fosphenytoin delivers the equivalent of one milligram of phenytoin sodium. Fosphenytoin Eugia contains 75 mg/mL of fosphenytoin sodium, which equals 50 mg PE/mL. This means that if a patient needs a 20 mg PE/kg loading dose, you use the same weight-based calculation as you would for phenytoin.
Cardiac monitoring is essential because phenytoin (the active metabolite of fosphenytoin) has direct effects on the cardiac conduction system. It can prolong the PR interval, widen the QRS complex, and depress atrioventricular conduction. Rapid intravenous administration has been associated with severe hypotension, bradycardia, heart block, ventricular tachycardia, ventricular fibrillation, and cardiac arrest, including fatal cases. Continuous ECG, blood pressure, and respiratory monitoring must be maintained throughout the infusion and for at least 30 minutes after completion. The infusion must be slowed or stopped if cardiovascular adverse effects are observed.
Yes, fosphenytoin can be given intramuscularly, which is a significant advantage over phenytoin (which cannot be given IM due to crystallization and tissue necrosis). IM fosphenytoin is well absorbed and achieves therapeutic phenytoin levels reliably. The IM route is particularly useful when IV access cannot be established, for maintenance dosing in hospitalized patients, and as a short-term substitute for oral phenytoin. Peak phenytoin levels after IM fosphenytoin are typically reached within 30 minutes to 3 hours. However, the IM route should not be used for status epilepticus because the time to peak therapeutic levels is too slow for this emergency indication.
The tingling, burning, or itching sensations (paresthesias and pruritus) that commonly occur during fosphenytoin infusion are caused by the fosphenytoin molecule itself, not by phenytoin. These sensations are most commonly felt in the groin, face, and extremities, and they are dose-rate dependent — meaning they occur more frequently at faster infusion rates. They are generally mild to moderate, self-limiting, and resolve within minutes of slowing or completing the infusion. These sensations are not allergic reactions and do not require discontinuation of the medication. Reducing the infusion rate is the standard approach to managing these symptoms.
References
- European Medicines Agency (EMA). Fosphenytoin – Summary of Product Characteristics. Available at: EMA.
- U.S. Food and Drug Administration (FDA). Cerebyx (Fosphenytoin Sodium Injection) – Prescribing Information. Pfizer Inc. Revised 2024.
- Trinka E, Cock HR, Hesdorffer D, et al. A definition and classification of status epilepticus – Report of the ILAE Task Force on Classification of Status Epilepticus. Epilepsia. 2015;56(10):1515–1523. doi:10.1111/epi.13121.
- Glauser T, Shinnar S, Gloss D, et al. Evidence-Based Guideline: Treatment of Convulsive Status Epilepticus in Children and Adults: Report of the Guideline Committee of the American Epilepsy Society. Epilepsy Curr. 2016;16(1):48–61. doi:10.5698/1535-7597-16.1.48.
- Kapur J, Elm J, Chamberlain JM, et al. Randomized Trial of Three Anticonvulsant Medications for Status Epilepticus (ESETT). N Engl J Med. 2019;381(22):2103–2113. doi:10.1056/NEJMoa1905795.
- National Institute for Health and Care Excellence (NICE). Epilepsies in children, young people and adults. NICE Guideline [NG217]. Updated 2024. Available at: NICE NG217.
- Temkin NR, Dikmen SS, Wilensky AJ, et al. A randomized, double-blind study of phenytoin for the prevention of post-traumatic seizures. N Engl J Med. 1990;323(8):497–502. doi:10.1056/NEJM199008233230801.
- British National Formulary (BNF). Fosphenytoin sodium. National Institute for Health and Care Excellence (NICE). 2025.
- World Health Organization (WHO). Model List of Essential Medicines – 23rd Edition. 2023. Available at: WHO EML.
- Meek PD, Davis SN, Collins DM, et al. Guidelines for nonemergency use of parenteral phenytoin products: proceedings of an expert panel consensus process. Arch Intern Med. 1999;159(22):2639–2644.
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