From the Guidelines
Symptoms of high Dilantin (phenytoin) levels, known as phenytoin toxicity, include dizziness, drowsiness, slurred speech, blurred or double vision, unsteady walking (ataxia), and involuntary eye movements (nystagmus) 1. These symptoms can occur due to the narrow therapeutic window of phenytoin (10-20 mcg/mL) and its saturated metabolism at higher doses, leading to disproportionately high blood levels 1. Some key points to consider:
- Phenytoin toxicity can cause confusion, nausea, vomiting, tremors, and in severe cases, seizures or coma 1.
- Physical signs may include gum overgrowth (gingival hyperplasia) with long-term use, skin rashes, and facial changes like coarsening of features 1.
- Elderly patients and those with liver disease are particularly susceptible to toxicity, even at therapeutic doses 1.
- If symptoms of phenytoin toxicity occur, it is essential to seek immediate medical attention for blood level monitoring and dose adjustment, as stopping Dilantin suddenly can trigger seizures 1. The most recent and highest quality study, published in 2014, provides evidence on the symptoms and management of phenytoin toxicity 1. Key considerations for management include:
- Monitoring serum phenytoin levels to avoid toxicity 1
- Adjusting doses based on serum levels and patient response 1
- Being aware of the potential for adverse effects, such as ataxia, nystagmus, and somnolence, especially with high doses or rapid infusion rates 1
From the FDA Drug Label
The initial symptoms are nystagmus, ataxia, and dysarthria. Other signs are tremor, hyperreflexia, lethargy, slurred speech, nausea, vomiting. Nystagmus, on lateral gaze, usually appears at 20 mcg/mL, ataxia at 30 mcg/mL; dysarthria and lethargy appear when the plasma concentration is over 40 mcg/mL
The symptoms of high Dilantin levels include:
- Nystagmus (usually appears at 20 mcg/mL)
- Ataxia (usually appears at 30 mcg/mL)
- Dysarthria (usually appears at plasma concentrations over 40 mcg/mL)
- Lethargy (usually appears at plasma concentrations over 40 mcg/mL)
- Tremor
- Hyperreflexia
- Slurred speech
- Nausea
- Vomiting 2
From the Research
Symptoms of High Dilantin
The symptoms of high dilantin, also known as phenytoin toxicity, can be severe and may include:
- Nausea and vomiting
- Central nervous system dysfunction, such as:
- Confusion
- Nystagmus (involuntary eye movements)
- Ataxia (loss of coordination and balance)
- Depressed conscious state, coma, and seizures in more severe cases
- Cardiac complications, such as arrhythmias and hypotension, although these are rare 3
- Cerebellar ataxia, which can be caused by long-term exposure to phenytoin, even at therapeutic doses 4
Clinical and Radiological Characteristics
Studies have shown that patients with epilepsy who take phenytoin are at risk of developing ataxia, with 40% of patients exhibiting clinical evidence of ataxia 4. MRI scans have also revealed structural, volumetric, and functional deficits of the cerebellum in patients with phenytoin-related ataxia 4.
Case Reports
Several case reports have highlighted the importance of therapeutic drug monitoring (TDM) and genetic considerations in preventing adverse drug reactions to phenytoin 5, 6. These reports demonstrate that patients can experience toxicity symptoms, including ataxia and seizures, despite taking standard doses of phenytoin.
Treatment and Management
The mainstay of therapy for phenytoin intoxication is supportive care, including attention to vital functions, management of nausea and vomiting, and prevention of injuries due to confusion and ataxia 3. There is no antidote for phenytoin toxicity, and treatment typically involves discontinuing the drug and providing supportive care.