This page contains brief details about the drug , it's indication, dosage & administaration, mechanism of action, related brands with strength, warnings and common side effects.

Background and Date of Approval

Fosphenytoin was initially approved by the United States Food and Drug Administration (FDA) on  September 30, 1996.

Mechanism of Action of undefined

fosphenytoin involves its conversion to the active drug phenytoin in the body. Phenytoin, a widely used anticonvulsant, works by stabilizing neuronal membranes and inhibiting excessive firing of neurons, thereby reducing abnormal electrical activity in the brain that can lead to seizures. This is achieved through multiple mechanisms, including modulation of sodium channels, which play a crucial role in generating and propagating nerve impulses. By influencing sodium channel kinetics and limiting their excitability, this medication and its active form, phenytoin, help prevent the uncontrolled neuronal firing characteristic of seizures.

Uses of undefined

Fosphenytoin is primarily used to manage and prevent seizures in various contexts, including controlling generalized tonic-clonic (grand mal) seizures, complex partial (psychomotor or temporal lobe) seizures, and as a second-line treatment for status epilepticus—a medical emergency characterized by prolonged or repeated seizures. It is also employed in seizure prevention during neurosurgery and serves as an alternative to oral phenytoin, particularly in emergencies where rapid seizure control is crucial.

undefined Drug administaration and Dosage available

Fosphenytoin is primarily administered intravenously (IV) or, in certain cases, intramuscularly (IM). Intravenous administration involves slowly infusing the medication into a vein, while intramuscular administration entails injecting it into a muscle. The route choice depends on factors such as the patient's condition, urgency of treatment, and accessibility of veins. Intravenous administration allows for rapid delivery, making it suitable for emergencies, while intramuscular administration provides an alternative when intravenous access is difficult. Proper technique and medical supervision are crucial for safe and effective administration, regardless of the chosen route.

Warnings, Precautions and Side Effects of undefined


The medication may lead to cardiac effects, including heart rhythm disturbances and hypotension. Liver problems, blood disorders, and respiratory depression are also possible. Fosphenytoin can affect mental alertness and coordination, potentially impairing activities like driving. Abruptly stopping this medication can increase seizure risk, and individuals with a history of drug-related rash (e.g., with phenytoin) are at a higher risk of developing a similar reaction. Its use includes potential bone health effects, such as decreased bone mineral density and an increased risk of osteoporosis, particularly with long-term use. Gum hypertrophy (enlargement) may occur, especially with prolonged treatment. This medication can lower vitamin D levels and affect calcium metabolism, potentially impacting bone health.


If you experience a skin rash, itching, swelling, or any signs of allergic reactions, promptly notify your healthcare provider. Discontinue fosphenytoin and seek medical attention if severe reactions occur. Individuals with heart conditions should be closely monitored for irregular heartbeats, dizziness, or fainting. Blood pressure should be regularly assessed during treatment. Regular liver function and blood cell count tests are essential, especially if you have a history of liver or blood disorders. Report any unusual symptoms to your doctor.Discuss bone health strategies with your healthcare provider, such as calcium and vitamin D supplementation and weight-bearing exercises, to mitigate potential bone-related effects.

Side Effects

Fosphenytoin use can lead to a range of side effects. Common side effects encompass gastrointestinal disturbances, skin reactions, fatigue, dizziness, muscle and joint pain, and changes in appetite. Serious side effects are rare but may include allergic reactions, neurological effects, eye-related symptoms, and potential liver impacts. Adhering to prescribed dosages, promptly reporting severe reactions, and consulting a healthcare provider is crucial to ensure this medication's safe and effective use.

Word Of Advice

Individuals with hypersensitivity to fosphenytoin or phenytoin should avoid its use, and vigilant monitoring for allergic reactions, cardiac effects, and hypotension is advised. Regular liver and kidney function assessments are crucial, especially in patients with pre-existing conditions. Blood disorders, respiratory issues, and potential interactions with alcohol and other medications should be carefully monitored and discussed with a healthcare provider. Pregnant or breastfeeding individuals should seek medical guidance due to potential fetal and infant risks. Activities requiring alertness, such as driving, may be impaired due to dizziness or drowsiness caused by this medication. Considerations extend to bone health, diet, mental health, and potential drug interactions, with medical oversight being particularly important for the geriatric and pediatric populations. Genetic factors, immunization effects, and proper storage should also be considered, along with formulating an emergency plan and using medical alert information.

Frequently Asked Question


  1. Pfizer Limited, US Food & Drug Administration, [Revised on 3/2017] [Accessed on 9th Aug 2023],
  2. Pfizer Limited, Electronic Medicines Compendium (EMC), [Revised on 15th Jun 2023] [Accessed on 9th Aug 2023],
  3. Roger J. Porter & Michael A. Rogawski, Antiseizure Drugs,  Lange’s Basic and Clinical Pharmacology, 14th Edition, 2018, 409-439.
  4. Misty D. Smith, Cameron S. Metcalf, and Karen S. Wilcox, Pharmacotherapy of the Epilepsies, Goodman & Gilman’s: The Pharmacological Basis of Therapeutics, 13th Edition, 2018, 303-326.


The drug information on this page is not a substitute for medical advice, it is meant for educational purposes only. For further details, consult your doctor about your medical condition to know if you can receive this treatment.