Dilantin (phenytoin sodium) is an anticonvulsant medication marketed by Pfizer, Inc. to prevent seizures in people in with epilepsy. Possible Dilantin side effects include phenytoin toxicity and a degenerative brain disorder called Cerebellar Atrophy.

About Dilantin

The U.S. Food & Drug Administration (FDA) approved Dilantin in 1953.  The drug is currently indicated to treat grand mal and temporal lobe seizures in patients with epilepsy, and to prevent and treat seizures associated with brain surgery.

Doctors may also prescribe this medication for certain types of arrythmias (irregular heart beat), neuropathic pain, and mood disorders like bipolar disorder.

While many other anticonvulsants have become available in the 60+ years since Pfizer launched Dilantin, it remains one of the most widely used medications in the world.

Phenytoin, the drug’s active ingredient, prevents seizures by decreasing electrical activity in the brain.

Patients should take this medication exactly as their doctor instructed. And they should NEVER stop treatment without talking to their physician, as doing so can cause serious withdrawal symptoms.

Common Dilantin Side Effects

The most common side effects associated with Dilantin include:

  • Headache
  • Nausea
  • Vomiting
  • Constipation
  • Dizziness or feeling of spinning
  • Drowsiness,
  • Trouble sleeping
  • Nervousness

Patients should talk to their doctors if these issues persist or become worse.

Like many anticonvulsants, Dilantin may cause depression, suicidal thoughts and behavior, and other mental health problems. As such, patients and caregivers should contact their doctor if they notice any changes in mood or behavior, including suicidal thoughts or signs of depression.

Phenytoin has also been associated with decreased bone density, which can lead to weak bones, osteoporosis and fractures. However, the risk is greatest when the medication is taken in conjunction with other anticonvulsants.

40% of patients taking Dilantin develop gingivitis, a condition that causes bleeding gums. Massaging the gums while brushing, flossing and regular dental checkups can minimize this problem.

Some people treated with phenytoin have experienced life-threatening hypersensitivity reactions, including Steven-Johnson Syndrome and toxic epidermal necrolysis.

Dilantin has also been linked to Purple Glove Syndrome, a skin disease that causes swelling, discoloration and pain in the arms and legs. The most serious cases can force amputation of affected limbs.

Phenytoin may cause birth defects (fetal hydantoin syndrome) when used by epileptic women during pregnancy.

Other serious Dilantin side effects include liver problems, low blood count, and high blood sugar.

Dilantin and Phenytoin Toxicity

People who take Dilantin for a long period of time are at risk for phenytoin toxicity, which occurs when the medication accumulates to dangerous levels in the body.

Signs of phenytoin toxicity include:

  • Nystagmus: Fast, uncontrollable eye movements or double vision.
  • Dizziness, drowsiness, or confusion
  • Lack of coordination in fingers, hands, arms, legs, or body
  • Slurred speech
  • Nausea or vomiting
  • Decreased appetite
  • Decreased activity
  • Abdominal bloating
  • Irregular jerky movements in children or the elderly

Dilantin and Cerebellar Atrophy

A growing number of Dilantin lawsuits claim that phenytoin toxicity can also cause severe tissue degeneration in the rear of the brain, a condition known as Cerebellar Atrophy. Though Pfizer was allegedly aware of this potential side effect in 2009, the company did not include any information about Cerebellar Atrophy on the drug’s label until 2016.

Prior to the label change, several studies had pointed to a link between phenytoin and Cerebellar Atrophy:

  • In 1990, researchers noted that patients taking phenytoin for more than 5 years experienced unsteady gait, speech problems and impaired muscle control due to cerebella nerve cell deficiencies in the brain.
  • A 1994 study indicated that long-term phenytoin patients developed smaller cerebellums overall compared to the placebo group.
  • In 2003, researchers reported that patients suffering from phenytoin toxicity experienced irreversible deterioration in their cerebellums.

Pregnant women, infants and the elderly apparently face a higher risk of phenytoin-induced Cerebellar Atrophy. The disorder occurs more frequently with long-term use and when when drug serum levels are above the therapeutic range.

  1. Pfizer (2019) “Dilantin Medication Guide” http://labeling.pfizer.com/ShowLabeling.aspx?id=546&section=MedGuide
  2. FDA (2016) “Phenytoin Drug Safety Labeling Changes” https://www.accessdata.fda.gov/scripts/cder/safetylabelingchanges/index.cfm?event=searchdetail.page&DrugNameID=134
  3. Reuters (2018) “Pfizer hit with multi-plaintiff suit over anti-seizure drug Dilantin” https://www.reuters.com/article/products-dilantin/pfizer-hit-with-multi-plaintiff-suit-over-anti-seizure-drug-dilantin-idUSL2N1WR2C4
  4. Acta Oncoligica (1999) “Stevens-Johnson Syndrome in Patients on Phenytoin and Cranial Radiotherapy” https://www.tandfonline.com/doi/pdf/10.1080/028418699431898
  5. JAMA Neurology (1994) “Cerebellar Atrophy in Patients With Long-term Phenytoin Exposure and Epilepsy” https://jamanetwork.com/journals/jamaneurology/article-abstract/592995
  6. Science Direct (2003) “Cerebellar volume and long-term use of phenytoin” https://www.sciencedirect.com/science/article/pii/S1059131102002674
Last Modified: April 29, 2019

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