From the Guidelines
Phenytoin overdose is characterized by dose-related adverse effects, including ataxia, nystagmus, tremor, and somnolence, which can progress to more severe symptoms such as confusion, lethargy, and coma. The signs and symptoms of phenytoin overdose can be attributed to its neurological, cardiovascular, and metabolic effects. Early signs of overdose include nystagmus, ataxia, slurred speech, and drowsiness 1. As toxicity progresses, patients may develop confusion, lethargy, and potentially coma.
Some of the key symptoms associated with phenytoin overdose include:
- Nystagmus (involuntary eye movement)
- Ataxia (poor coordination)
- Tremor
- Somnolence (drowsiness)
- Confusion
- Lethargy
- Coma
- Cardiovascular symptoms such as hypotension, bradycardia, and cardiac arrhythmias are also possible 1.
It is essential to note that phenytoin toxicity often correlates with serum levels above 20 mcg/mL, with severe symptoms typically appearing above 30-40 mcg/mL. The drug's nonlinear pharmacokinetics mean small dose increases can cause disproportionately large increases in blood levels. Treatment involves discontinuing the medication, supportive care, and possibly activated charcoal for recent ingestions. Healthcare providers should monitor phenytoin levels in patients on this medication, especially when adjusting doses or adding interacting medications, to prevent toxicity 1.
From the FDA Drug Label
The most common manifestations encountered with phenytoin therapy are referable to this system and are usually dose-related. These include nystagmus, ataxia, slurred speech, decreased coordination, and mental confusion Dizziness, insomnia, transient nervousness, motor twitchings, paresthesias, somnolence and headaches have also been observed. Serum levels of phenytoin sustained above the optimal range may produce confusional states referred to as "delirium," "psychosis," or "encephalopathy," or rarely irreversible cerebellar dysfunction.
The signs and symptoms of phenytoin overdose include:
- Nystagmus
- Ataxia
- Slurred speech
- Decreased coordination
- Mental confusion
- Dizziness
- Insomnia
- Transient nervousness
- Motor twitchings
- Paresthesias
- Somnolence
- Headaches
- Confusional states (delirium, psychosis, or encephalopathy)
- Irreversible cerebellar dysfunction 2 2
From the Research
Signs and Symptoms of Phenytoin Overdose
The signs and symptoms of phenytoin (Dilantin) overdose include:
- Nausea
- Central nervous system dysfunction, such as:
- Confusion
- Nystagmus
- Ataxia
- Depressed conscious state
- Coma
- Seizures (in more severe cases)
- Cardiac complications, such as:
- Arrhythmias
- Hypotension (rare, but may occur with parenteral administration of phenytoin or fosphenytoin) 3
- Ataxia, giddiness, and vomiting have also been reported in cases of phenytoin overdose 4
- Other symptoms, such as agitation, abnormal gait, and hallucinations, have been observed in patients with phenytoin toxicity 5
Treatment and Management
Treatment for phenytoin overdose is primarily supportive care, including:
- Attention to vital functions
- Management of nausea and vomiting
- Prevention of injuries due to confusion and ataxia
- Activated charcoal may be considered if the patient presents early, but its effectiveness is controversial 3
- Hemodialysis and hemoperfusion may be used in severe cases, particularly with intravenous overdose 6
- Plasmaphoresis has been used in some cases, but its effectiveness is not well established 7