The antiepileptic drug Dilantin (phenytoin) is associated with cerebellar atrophy—a devastating condition that impacts motor function, coordination, memory, and speech. Despite knowing that the drug potentially causes damage to the cerebellum, Pfizer and other manufacturers aggressively marketed it for decades without warning about this side effect. Several plaintiffs are suing drugmakers over their failure to warn doctors and patients about Dilantin-induced cerebellar atrophy.
Research Links Dilantin to Cerebellar Degeneration
Dilantin is the trade name of phenytoin, a drug used to treat many epilepsy syndromes. The drug was first formulated in the 1930s and the drug company Parke Davis gained FDA approval for Dilantin in 1953.
As early as the 1960s, researchers began investigating possible cerebellar dysfunction associated with phenytoin toxicity. Numerous studies have noted that patients taking the drug experienced nerve cell loss in the cerebellum (the part of the brain that coordinates movement).
One complicating factor, however, is that seizure disorder itself can cause cerebellar atrophy, which makes it difficult to determine whether the patient’s underlying condition or Dilantin is to blame. A 1994 study controlled for this factor by placing half of the participants on Dilantin and the other half on an alternative treatment. The study found significantly more pronounced cerebellar atrophy in Dilantin-exposed patients than in the non-Dilantin patient group.
Other studies have similarly suggested that cerebellar degeneration may be a chronic adverse effect of phenytoin therapy. It is estimated that approximately 1 out of 3 patients undergoing long-term phenytoin therapy will develop cerebellar atrophy. Affected patients typically show cerebellar volume loss on CT and MRI scans.
Symptoms of Cerebellar Atrophy
Cerebellar atrophy is a loss of nerve cells, or neurons, in the cerebellum. As cerebellar neurons degenerate, a patient’s motor function, coordination, memory, and ability to speak are affected. Symptoms of cerebellar atrophy include:
- Balance issues
- Slurred speech
- Stroke-like symptoms
- Quivering of the torso
- Jerky arm or leg movements
- Small, rapid movements in the eye
- Memory loss
These symptoms may be diagnosed as “ataxia,” a condition marked by impaired coordination due to nerve damage. Patients exhibiting symptoms of cerebellar atrophy may undergo neuroimaging using CT or MRI scans.
In some cases, stopping Dilantin treatment has allowed the symptoms to resolve. In other cases, Dilantin toxicity injuries to the brain may be permanent. If you or a loved one is taking Dilantin and experiencing possible symptoms of cerebellar atrophy, DO NOT stop treatment without consulting a doctor. Usually, patients start taking a new seizure medication while still on the old one under close physician supervision.
Previous Dilantin Lawsuits
This is not the first time that Dilantin manufacturers have been accused of failing to warn about serious drug side effects. Previously, Pfizer was hit with lawsuits alleging that Dilantin causes a drug-induced condition known as toxic epidermal necrolysis (TEN) that results in a severe rash, peeling skin, fever, and sores.
The parents of a nine-year old girl who died as a result of Dilantin-related TEN received a $3.78 settlement from Pfizer. Attorneys for the girl’s parents said that Pfizer did not warn doctors and patients in the United States that Dilantin could cause skin disease, even though warnings were provided in Canada and other countries.
Dilantin Warning Labels
Drug manufacturers have a legal duty to warn prescribers and users of potential drug side effects. Failure to do so can be grounds for legal action against the manufacturer.
Dilantin warning labels have been updated several times over the last decade, including a new warning for serious dermatologic reactions. Current Dilantin labeling also warns about suicidal thoughts and behaviors, hypersensitivity, heart, kidney, and liver effects, decreased bone mineral density, and fetal harm.
Ataxia is not listed under Dilantin Warnings and Precautions, although “nervous system reactions” and ataxia are listed under “Adverse Reactions.” The label notes that such reactions are “usually dose-related.”
Whether Dilantin-induced cerebellar atrophy is indeed “dose-related” could be a key point in Dilantin lawsuits. Some studies have found that cerebellar ataxia occurs at therapeutic-range phenytoin usage. If this is the case, it could be argued that current Dilantin warnings are not strong enough.
Many researchers have also pointed out the need for Therapeutic Drug Monitoring (TDM) when phenytoin is administered for seizures in order to avoid possible toxic effects. This raises questions about whether Pfizer was proactive enough about warning doctors of the need for Dilantin TDM.
According to lawsuits filed against Pfizer and its subsidiaries Parke-Davis, Pharmacia, and Warner-Lambert, the drug companies have been aware of the risk of cerebellar atrophy from Dilantin since at least 2009, but only added warnings to U.S. consumer warning labels in 2016.
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