Phenytoin (Efficacy)

Phenytoin, sold under the brand name Dilantin among others, is an anti-seizure medication. It is a compound approved by the FDA in 1953 for the prevention of seizures. It acts by blocking undesired brain activity by reducing the electric conductivity between the neurons, blocking voltage sensitive sodium channels. By blocking the cardiac solium channels, phenytoin acts as an antiarrhythmic agent.

Phenytoin can be used alone or in combination with other anticonvulsive drugs such as phenobarbital. It can also be used to prevent seizures that happen during surgery but it is not used in absence seizures (petit mal).

The clinical management of phenytoin is more complicated than in other anticonvulsant drugs because it has a non lineal pharmacokinetic; it binds in great measure to the plasma proteins and has a high interindividual variability in its bioavailability.

Mechanism of action: anticonvulsant drugs raise the threshold of the seizures and/ or reduce their intensity. Phenytoin acts by limiting the diffusion of the discharges and their spread in contrast to phenobarbital and carbamazepine that raise the threshold of the seizures. For this reason, phenytoin is less effective preventing the seizures produced by drugs or electro-induced seizures. The effects of phenytoin depend on its action on the sodium channels of the neuronal cell membrane. Its anticonvulsive effects have less sedating effects than phenobarbital. In large doses, phenytoin causes excitability and induces seizures. Because of its effects on the sodium channels, phenytoin is slightly antiarrhythmic, acting on the Purkinje fibers.


  • Dilantin®
  • Infatabs®
  • Kapseals®


Phenytoin can produce considerable mental health disorders and therefore, the doctor, the patient and the patient's family should carefully evaluate the risk-benefit of treatment with this drug.

Other side effects may be normal and become serious or they may be serious on their own. In all cases, it is convenient to consult the medical professional if the side effects appear or last for a length of time.

The most frequent side effects are:

  • Headache and dizziness
  • Confusion (avoid driving motor vehicles or using machinery)
  • Difficulty speaking and thinking
  • Loss of coordination of body movements, especially eye movements
  • Nausea and vomiting
  • Swelling of lips and gums
  • Elevated levels of blood sugar
  • Constipation
  • Unusual hair growth

Among the side effects considered serious are:

  • Fever
  • Joint pain
  • Swollen glands
  • Severe skin reaction (skin pain, followed by a red or purple skin rash that spreads (especially in the face or upper body) blistering and peeling
  • Jaundice (yellowing of the skin or eyes)
  • Pain in the upper ride side of the stomach
  • Easy bruising or sudden bleeding
  • Excessive fatigue
  • Flu-like symptoms
  • Loss of appetite
  • Bone pain


Get emergency medical help if you have any of these signs of an allergic reaction: hives; difficulty breathing; swelling of your face, lips, tongue, or throat. You may be more likely to have an allergic reaction if you are African-American.

Report any new or worsening symptoms to your doctor, such as: mood or behavior changes, depression, anxiety, or if you feel agitated, hostile, restless, hyperactive (mentally or physically), or have thoughts about suicide or hurting yourself.

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