API: Phenytoin Sodium

What Is Phenytoin Sodium and How Does It Work?

Phenytoin Sodium is an anticonvulsant that is thought to act by preferentially binding to the inactive form of sodium channels. This, in turn, causes a time-dependent, voltage-dependent and use-dependent block of the channel, particularly against repetitive firing of action potentials, thereby inhibiting both seizure spread and propagation.1 Phenytoin sodium in known to have class IB antiarrhythmic properties due to its effect on sodium channels in both cardiac myocyte and Purkinje fiber cell membranes.2 Phenytoin Sodium also has muscle relaxation properties, potentially due to a reduction in the sensitivity of muscle spindles stretching, again due to limited to ion channel transport.3

For more information, including a MSDS sheet, please see PNA’s Phenytoin Sodium page.

Approved Indications4

  • Seizures: Phenytoin Sodium is used to control generalized tonic-clonic seizures, to pre-treat or control partial seizures, and to treat or prevent seizures occurring during neurosurgery.
  • Anti-arrhythmia: Phenytoin Sodium is used to control ventricular arrhythmias, particularly in postoperative patients and those with a long Q-T interval. Intravenous use of the drug may also help treat seizures due to cardiac glycoside intoxication.
  • Pain control: Phenytoin Sodium may be effective in treating chronic pain due to peripheral neuropathic syndromes.
  • Note: This drug is not indicated for treatment of pure absence seizures and may cause increased seizure activity in those cases. Phenytoin Sodium may be prescribed as an adjunct treatment of combined absence and tonic-clonic seizures.

Side Effects and Drug Interactions

Common side effects in patients taking Phenytoin Sodium include5:

  • Anxiety
  • Changes in heartbeat
  • Chest pain or discomfort
  • Cold, clammy, or pale skin
  • Decreased coordination
  • Disorientation, dizziness, or drowsiness
  • Fatigue
  • Hallucinations
  • Headaches or lightheadedness
  • Mood changes
  • Nausea
  • Pain in the shoulders, back, neck, or jaw
  • Problems breathing
  • Slurred speech
  • Sweating
  • Swelling of the feet and lower legs
  • Uncontrolled eye movements

Patients who suffer from severity of these common side effects should contact their pharmacist or physician right away. Patients who experience drug overdose (change in consciousness or speech patterns, fainting, ears, or unusual fatigue) should inform their physician immediately.

Patients who are allergic to phenytoin sodium should not take this drug. Drug interactions are also widespread and should be discussed on a case-by-case basis for maximum risk/reward.

Phenytoin sodium can affect a number of medical conditions, including:


  • Blood Dyscrasias
  • Liver Disease
  • Porphyria
  • Renal Dysfunction
  • Cardiotoxicity
  • Suicidal Tendency
  • Hyperglycemia
  • Megaloblastic Anemia
  • Osteomalacia
  • Thyroid Function Tests

Latest News and Research

Phenytoin Sodium was developed in 1908 and first used in the 1930s for treating seizures. The drug is currently on the World Health Organization’s (WHO) List of Essential Medicines.6 This list, which is updated every two years, includes drugs that the WHO defines to “satisfy the health care needs of the majority of the population; they should therefore be available at all times in adequate amounts and in appropriate dosage forms, at a price the community can afford.”

Phenytoin Sodium may also have activity against multiple sclerosis, and in particular is being studied for its ability to halt nerve damage before it even starts.7 The sodium channel blocking properties may alternatively be used to reduce migration and invasion of certain cancer cells in metastatic breast cancer.8

Along yet another line, Phenytoin Sodium is also currently in clinical trials to see if it can prevent negative effects in patients taking megestrol, which is typically prescribed to stimulate appetite in medically ill or elderly patients who may be at risk for cognitive impairment.9

Buying Guide

PNA is a recommended bulk supplier of Phenytoin Sodium and other APIs. You can learn more about Phenytoin Sodium here.

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Show 9 footnotes

  1. “Dilantin,” 2016, http://www.rxlist.com/dilantin-drug/clinical-pharmacology.htm
  2. “Phenytoin: an old but effective antiarrhythmic agent for the suppression of ventricular tachycardia,” 2013, https://www.mja.com.au/journal/2013/199/3/phenytoin-old-effective-antiarrhythmic-agent-suppression-ventricular-tachycardia
  3. “Phenytoin,” September 16, 2013, http://www.drugbank.ca/drugs/DB00252
  4. “Phenytoin Sodium,” January 4, 2016, http://www.drugs.com/monograph/phenytoin-sodium.html
  5. “Phenytoin Sodium Side Effects,” January 4, 2016, http://www.drugs.com/sfx/phenytoin-sodium-side-effects.html?form=injection_solution
  6. “WHO Model Lists of Essential Medicines,” August 2015, http://www.who.int/medicines/publications/essentialmedicines/en/
  7. “The next breakthrough in MS Research – Phenytoin to halt disability progression?” July 11, 2013, https://www.mssociety.org.uk/ms-resources/next-breakthrough-ms-research-phenytoin-halt-disability-progression
  8. “Therapeutic potential for phenytoin: targeting Nav1.5 sodium channels to reduce migration and invasion in metastatic breast cancer,” June 8, 2012, http://link.springer.com/article/10.1007/s10549-012-2102-9
  9. “Phenytoin for Memory Impairment Secondary to Megestrol,” 2016, http://www.utsouthwestern.edu/labs/psychoneuroendocrine/research/phenytoin.html