Does Dilantin Cause Tremors?
Yes, Dilantin (phenytoin) can cause tremor as a recognized adverse effect. Tremor is explicitly listed among the common side effects in the FDA drug label 1.
Evidence from FDA Drug Labeling
The official FDA prescribing information for Dilantin clearly identifies tremor as one of the most common side effects 1. The drug label also describes a broader spectrum of movement-related adverse effects under central nervous system complications, including:
- Motor twitchings
- Tremor (specifically listed)
- Dyskinesias (chorea, dystonia, asterixis)
- Ataxia and decreased coordination
- Paresthesias
These movement disorders are documented in the "Adverse Reactions" section, with tremor appearing among the frequently reported side effects alongside problems with walking and coordination, slurred speech, confusion, and dizziness 1.
Mechanism and Clinical Context
The FDA label notes that phenytoin can induce various involuntary movements, including "rare reports of phenytoin-induced dyskinesias, including chorea, dystonia, tremor, and asterixis, similar to those induced by phenothiazine and other neuroleptic drugs" 1. Research confirms that involuntary movements, while infrequent, are a recognized complication of phenytoin treatment, with the mechanism likely involving variable effects on dopamine metabolites and serotonergic activity 2.
Important Clinical Considerations
Dose-related effects: Most central nervous system manifestations with phenytoin are dose-related 1. However, tremor can occur even at therapeutic levels.
Long-term complications: Chronic phenytoin use is associated with more severe cerebellar dysfunction. Studies show that 40% of patients on long-term phenytoin develop cerebellar ataxia, with gait disturbances being predominant features 3. Even patients without clinical ataxia may have reduced cerebellar volume on imaging.
When to be concerned: If tremor develops or worsens on phenytoin, consider:
- Checking phenytoin levels (though tremor can occur at therapeutic levels)
- Evaluating for other cerebellar signs (ataxia, coordination problems, slurred speech)
- Assessing whether the tremor is postural (as described in case reports) 2
- Considering alternative antiepileptic medications if tremor is functionally limiting
The tremor associated with phenytoin is a well-documented adverse effect that should prompt clinical evaluation and potentially medication adjustment or substitution.