Phenytoin toxicity: Difference between revisions
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==Background== | ==Background== | ||
*Mortality is extremely rare after intentional overdose if good supportive care is provided | *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) | *Rapid IV dosing carries greatest risk (due to propylene glycol constituent of IV form → myocardia depression & cardiac arrest) | ||
*90% protein bound; dialysis ineffective | *90% protein bound; dialysis ineffective | ||
==Clinical Features== | ==Clinical Features== | ||
*CV (only with IV form) | *CV (only with IV form) | ||
**Bradycardia | **[[Bradycardia]] | ||
**Hypotension | **[[Hypotension]] | ||
**Asystole | **[[Vfib]] | ||
*Neuro | **[[Asystole]] | ||
**Nystagmus | *Neuro | ||
***First only with forced lateral gaze; later becomes spontaneous | **[[Nystagmus]] | ||
***First only with forced lateral gaze; later becomes spontaneous | |||
***May disappear at higher levels | ***May disappear at higher levels | ||
**Ataxia | **[[Ataxia]] | ||
**Decreased LOC | **Decreased LOC | ||
*GI | *GI | ||
** | **[[Nausea and vomiting]] | ||
*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% | |||
==Diagnosis== | ==Differential Diagnosis== | ||
== | |||
# | ==Evaluation== | ||
{{Phenytoin toxicity level chart}} | |||
*[https://www.mdcalc.com/phenytoin-dilantin-correction-albumin-renal-failure#evidence| 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 toxicity|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 bradyarrhythmia: | |||
**[[ACLS: Bradycardia]], Atropine, epinephrine, dopamine are first line | |||
**May consider [[transcutaneous pacing|transcutaneous]] or [[transvenous pacing]] | |||
*Hypotension | |||
**IVF bolus | |||
*Detoxification | |||
**[[Activated charcoal]] PO | |||
**[[Gastric lavage]] and [[whole bowel irrigation]] are '''NOT''' recommended | |||
==Disposition== | ==Disposition== | ||
*Cannot base on phenytoin level (erratic absorption after PO overdose) | *Cannot base on phenytoin level (erratic absorption after PO overdose) | ||
**Consider discharge if | **Consider discharge if patient has only mild symptoms and serial phenytoin levels decline | ||
==See Also== | |||
*[[Phenytoin]] | |||
== | ==References== | ||
<references/> | |||
[[Category: | [[Category:Toxicology]] | ||
Latest revision as of 15:08, 21 May 2020
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)
- Neuro
- 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 bradyarrhythmia:
- 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