Fosphenytoin vs Phenytoin – Which Anticonvulsant Medicine Works Best?

Fosphenytoin belongs to a group of medicines called anticonvulsants that work by slowing down impulses in the brain which cause seizures.

A seizure is a brief episode of symptoms caused by a surge of abnormal electrical activity in the brain. It usually causes seizures, that can affect the behavior or the way a sufferer sees things around him for a short time.


It is used for the treatment and prevention of seizures that are occurring during neurosurgery. Also, it is used for the control of generalized tonic-clonic status epilepticus and other conditions.

Status epilepticus is a condition when seizures occur close together and the person doesn’t recover from a seizure or when a seizure lasts longer than 5 minutes. Only about 1 of 4 people who have seizures or status epilepticus have epilepsy.

Epilepsy is a central nervous system condition in which brain activity becomes abnormal, leading to periods of unusual behavior or seizures and occasionally, the loss of awareness.

However, approximately 15 percent of epileptic patients will have a status epilepticus (SE) episode at some point during their lives. Usually, it happens when they are not controlling their condition with drugs.


This medicine may be given as an infusion into a vein or as an injection into a muscle. To prevent seizures or for nonemergent therapy, 15 to 30 mg per kg can be administered intramuscularly or intravenously in a loading dose, followed by a daily maintenance dosage of 6 to 12 mg per kg.

For sufferers with SE, 22.5 to 30 mg per kg of this medicine should be used intravenously at a rate of 100 to 150 mg per minute.

Side Effects And Precautions

Common side effects may include:

  • pain in the back or hips;
  • ringing in the ears;
  • loss of coordination;
  • muscle weakness;
  • tremor;
  • mild itching;
  • drowsiness;
  • dizziness;
  • headache;
  • dry mouth;
  • mild nausea;
  • constipation.

Rare side effects may include:

  • easy bleeding;
  • easy bruising;
  • skin rash;
  • flu symptoms;
  • body aches;
  • swollen glands;
  • fever;
  • feeling short of breath;
  • irregular heart rhythm;
  • chest pain;
  • vision or speech problems;
  • skin discoloration anywhere in the body;
  • severe burning.

You should not use this medicine if you have certain serious heart conditions, like – heart block, slow heartbeats, Adams-Stokes syndrome (a heart rhythm disorder), or AV block, as well as if you also take Rescriptor (delavirdine).

Consuming alcoholic beverages can change the amount of this medicine that stays in the body, plus, how the drug works.

When using this drug, avoid using birth control pills and other hormone-based birth control (like – intrauterine device) because they may not be so effective at preventing a pregnancy.

In the US, more than 1 million women of child-bearing age have had epilepsy diagnosed. Nevertheless, less than 1 percent of all pregnancies are complicated by seizure conditions. In the present day, there are no controlled data in human pregnancy regarding the safe use of this medicine.

However, administration of this medication to pregnant animals resulted in increased incidences of behavioral abnormalities and fetal malformations.


It is an anti-epileptic medicine that is used to treat epilepsy. It works by stabilizing electrical activity in the brain. The first production of this drug was in 1908, and in 1936, Heinrich Biltz, a German professor, and chemist, found it useful for seizures.

Its brand name is Dilantin, and in 1953, it was originally approved for use in seizures by the FDA. It is manufactured by Pfizer, Inc, an American pharmaceutical corporation with headquarters in New York City, USA.


It is a prescription medication that is used to treat complex partial (temporal lobe or psychomotor) seizures, tonic-clonic seizures, as well as to treat and prevent seizures during or after brain surgery.


The dose of this drug varies from individual to individual and it is depending on the condition being treated. It is available as:

  • Liquid medicine – 90 mg in 5mL and 30 mg in 5 mL;
  • Infatabs – 50 mg;
  • Capsules – 25 mg, 50 mg, 100 mg, 300 mg;
  • Tablets – 100 mg.

The extended-release capsules are recommended to be taken 1 to 4 times per day. The suspension and chewable tablets are generally taken 3 times per day. You should take this medicine with a full glass of water unless your healthcare provider tells you otherwise.

Side Effects And Precautions

Common side effects may include:

  • nervousness;
  • decreased coordination;
  • dizziness;
  • mental confusion;
  • slurred speech;
  • nervousness;
  • sleep problems;
  • tender gums;
  • breathing problems;
  • problems with speaking;
  • drowsiness;
  • problems with muscle coordination or control;
  • spinning sensation;
  • headache;
  • trembling;
  • unsteadiness;
  • constipation;
  • vomiting;
  • nausea.

Rare side effects may include:

  • unusual eye movements;
  • skin rash;
  • worsening seizures;
  • unusual behavior;
  • easy bruising;
  • an unexplained sore throat;
  • blurred vision;
  • joint pain.

In some patients, this medicine may cause thoughts of suicide or self-harm. Contact your healthcare professional as soon as this happens. Also, it is not recommended to consume alcoholic beverages while using this medication.

Fosphenytoin vs Phenytoin – Which Anticonvulsant Medicine Works Best?

Fosphenytoin has a more rapid intravenous administration rate and a better tolerability which actually makes it effective for loading doses. However, it is used only for a short time when other forms of phenytoin are not available or cannot be given.

Furthermore, fosphenytoin is converted to phenytoin, which is an acknowledged cause of acute idiosyncratic drug-induced liver disease.

Images credit – @Getty & Shutterstock

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