Drug information of Mephenytoin


Mephenytoin is a drug used to control seizures. It works by slowing down impulses in the brain that cause seizures.
Mephenytoin is usually reserved for seizure conditions that have not responded to other less toxic antiseizure medicines

Mechanism of effect

The mechanism of action of mephenytoin is not definitely known, but extensive research strongly suggests that its main mechanism is to block frequency-, use- and voltage-dependent neuronal sodium channels, and therefore limit repetitive firing of action potentials.


Mephenytoin is an antiepileptic drug which can be useful in the treatment of epilepsy. The primary site of action appears to be the motor cortex where spread of seizure activity is inhibited. Possibly by promoting sodium efflux from neurons, mephenytoin tends to stabilize the threshold against hyperexcitability caused by excessive stimulation or environmental changes capable of reducing membrane sodium gradient. This includes the reduction of posttetanic potentiation at synapses. Loss of posttetanic potentiation prevents cortical seizure foci from detonating adjacent cortical areas. Mephenytoin reduces the maximal activity of brain stem centers responsible for the tonic phase of tonic-clonic (grand mal) seizures.


Volume of distribution:
1.4 L/kg
Protein binding and absorption:
Not Availablei
Approximately 7 hours
Not Available
Nirvanol-S-4-Hydroxymephenytoin-S-Nirvanol-4'-HydroxymephenytoinAbsorption: Absorbed from the GI tract.

Drug indications

Generalized tonic-clonic or complex-partial seizures


Adults: 50 to 100 mg P.O. daily; may increase by 50 to 100 mg at weekly intervals. Usual maintenance dosage is 200 to 600 mg daily in three equally divided doses. Doses up to 800 mg daily may be required.
Children: Initial dose is 50 to 100 mg P.O. daily. May increase slowly by 50 to 100 mg at weekly intervals. Dosage must be adjusted individually. Usual maintenance dosage is 100 to 400 mg daily (or 3 to 15 mg/kg daily or 100 to 450 mg/m2/day) in three equally divided doses

Side effects

an allergic reaction (difficulty breathing; closing of your throat; swelling of your lips, tongue, or face; or hives);
slurred speech or staggering walk;
a rash;
changes in vision;
yellow skin or eyes (jaundice);
easy bruising or bleeding; or
swollen or tender gums

nausea, vomiting, constipation, or diarrhea;

mild dizziness or drowsiness;

tender or swollen glands;


muscle twitches;

increased facial hair;

swelling of the breasts; or



Before taking this medication, tell your doctor if you have kidney or liver disease. You may not be able to take mephenytoin, or you may require a lower dose or special monitoring during treatment
Mephenytoin may increase blood sugar. If you are a diabetic and are taking mephenytoin, watch for changes in your blood sugar levels that may be caused by this medication.
Do not drink alcohol while taking this medication. Alcohol can cause deep sedation or sleepiness. It may also increase your risk of having seizures

Points of recommendation

-Do not change the brand, generic formulation, or dosage of this medication without first talking to your doctor.
-Do not stop taking your medication even if you feel better. It is important to continue taking mephenytoin to prevent your seizures from recurring.
-Take each dose of mephenytoin with a full glass of water.
-Store this medication at room temperature away from light and moisture.
-Take the missed dose as soon as you remember. However, if it is almost time for your next dose, skip the dose you missed and take only your next regularly scheduled dose. Do not take a double dose of this medication

Pregnancy level


Mephenytoin is in the FDA pregnancy category C. This means that it is not known whether mephenytoin will harm an unborn baby. Do not take mephenytoin without first talking to your doctor if you are pregnant.

Breast feeding warning

Mephenytoin passes into breast milk and may affect a nursing infant. Do not take mephenytoin without first talking to your doctor if you are breast-feeding a baby

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