We need you! Join our contributor community and become a WikEM editor through our open and transparent promotion process.
Phenytoin toxicity
From WikEM
Contents
Background
- Mortality is extremely rare after intentional overdose if good supportive care is provided
- Rapid IV dosing carries greatest risk (due to propylene glycol constituent of IV form → myocardia depression & cardiac arrest)
- 90% protein bound; dialysis ineffective
Clinical Features
- CV (only with IV form)
- Bradycardia
- Hypotension
- Vfib
- Asystole
- Neuro
- Nystagmus
- First only with forced lateral gaze; later becomes spontaneous
- May disappear at higher levels
- Ataxia
- Decreased LOC
- Nystagmus
- GI
- Skin
- tissue infiltration (IV) → "Purple glove syndrome"
- edema, pain, ischemia, tissue necrosis, compartment syndrome
- Anticonvulsant hypersensitivity syndrome
- Fever, eosinophilia, rash, pseudolymphoma, SLE, pancytopenia, hepatitis, pneumonitis, pharyngitis, rhabdomyolysis
- Mortality rate of 10%
Differential Diagnosis
Evaluation
Toxicity symptoms by phenytoin level^
| Level | Sypmtoms |
| >10 | Usually no symptoms |
| 10-20 | Occasional mild nystagmus |
| 20-30 | Nystagmus |
| 30-40 | Ataxia, slurred speech, Nausea/vomiting |
| 40-50 | Lethargy, confusion |
| >50 | Coma, seizure (rare) |
^Provides a rough guide only; neither sensitive nor specific
- Correct for albumin level
- Free phenytoin concentration determines toxicity
- Hypoalbuminemia results in higher free phenytoin concentration
- Other laboratory testing
- LFTs, hepatic dysfunction increases risk of phenytoin toxicity
- CBC, frequently show eosinophilia or marked leukocytosis
- Total CK
- ECG, may see arrhythmias, AV block, or sinus arrest with junctional or ventricular escape
- POC glucose, rule out hypoglycemia as cause of AMS
- Acetaminophen and salicylate levels, rule out common coingestion
- Urine pregnancy test
Management
- Supportive care is mainstay of treatment
- If intubation needed, standard RSI meds ok, avoid lidocaine (same antidysrhythmic properties as phenytoin)
- If symptomatic bradydysrhythmia:
- ACLS: Bradycardia, Atropine, epinephrine, dopamine are first line
- May consider transcutaneous or transvenous pacing
- Hypotension
- IVF bolus
- Detoxification
- Activated charcoal PO
- Gastric lavage and whole bowel irrigation are NOT recommended
Disposition
- Cannot base on phenytoin level (erratic absorption after PO overdose)
- Consider discharge if patient has only mild symptoms and serial phenytoin levels decline
