See also
Poisoning – Acute guidelines for initial management
Resuscitation
Key Points
- Phenytoin intoxication is usually benign and symptoms are dose-related
- Rapid IV administration may result in cardiac arrhythmias due to the propylene glycol contained in the formulation and not due to the phenytoin itself
- There is good correlation between serum concentrations and clinical manifestations, but this cannot be used to predict duration of symptoms
For 24 hour advice, contact Victorian Poisons Information Centre 13 11 26
Background
Clinical features of phenytoin overdose include neurological and gastrointestinal symptoms. Onset of symptoms is usually within 1 to 2 hours of ingestion, or within minutes if IV administration. There can be a delay by up to five days for the maximal effects following oral ingestion due to zero-order kinetics and prolonged absorption.
Children requiring assessment
All children with deliberate self-poisoning or significant (>20 mg/kg OR >10 mg/kg greater than the child’s usual daily dose if on a regular dose) accidental ingestion
Any symptomatic child
Acute ingestion of unknown quantity
Any child where the developmental age is inconsistent with accidental poisoning as non-accidental poisoning should be considered.
Risk Assessment
History
Intentional overdose or accidental
Dose:
-
Stated or likely dose taken
- Presented as syrup, immediate release capsules or chewable tablets
-
If possible determine the exact name and tablet size
-
Calculate the maximum possible dose per kg
Co-ingestants eg paracetamol
Examination
- CNS
- Nystagmus, dysarthria, ataxia, tremor, drowsiness, involuntary movements, seizures, coma
- GIT
- Other
- Massive ingestion: Hypernatraemia and hyperglycaemia
- Rapid IV administration: hypotension, bradycardia, arrhythmias
Always check for Medicalert bracelet in any unconscious patient, or any other signs of underlying medical condition (fingerprick marks etc)
Consider the possibility of co ingestions, either accidental or deliberate
Investigations
ECG: (particularly if IV administration) initially and repeat at 6 hours until normal.
Phenytoin serum concentration
Toxic concentration
- 40 to 80 umol/L (10 to 20 mg/L) - Therapeutic
- 80 to 120 umol/L (20 to 30 mg/L) - Horizontal nystagmus
- 120 to 160 umol/L (30 to 40 mg/L) - Vertical nystagmus, diplopia, ataxia, slurred speech, tremor, hyperreflexia, drowsiness, nausea, vomiting
- 160 to 200 umol/L (40 to 50 mg/L) - Confusion, disorientation, lethargy, hyperactivity, mania, respiratory depression
- > 200 umol/L (50 mg/L) - Extreme lethargy, coma, paradoxical seizures
BSL
Paracetamol concentration in all intentional overdoses
Acute Management
Children Requiring Treatment
- All symptomatic children
- Acute ingestion of unknown quantity
- Based on ingestion amount:
- Phenytoin ingestion of >20 mg/kg OR >10 mg/kg greater than the child’s usual daily dose if patient on maintenance treatment phenytoin treatment
- Standard procedures and supportive care
Decontamination
- Decontamination is not usually required in phenytoin overdose
Mild symptoms
- Observe 6 hours post-exposure, discharge once symptom-free
Moderate-to-severe or persistent symptoms after 6 hours of observation
(eg Depressed conscious state or cardiac arrhythmias)
- Admit for observation and supportive management
- Repeat blood drug concentration at 6 hours if ongoing symptoms
- If drug concentration increasing or above therapeutic range, admit for ongoing observation and serial drug concentration monitoring in consultation with toxicologist
- Discussion with paediatric intensive care team (put in the standard PIPER contact details) if severe symptoms
When to admit/consult local paediatric team, or who/when to phone
Admission should be considered for all children and young people with an intentional overdose or in patients with persisting symptoms after 6 hours observation
Consult Contact Victorian Poisons Information Centre 13 11 26 for advice
When to consider transfer to a tertiary centre
Children with severe symptoms with the potential to require intensive care review
For emergency advice and paediatric or neonatal ICU transfers, call the Paediatric Infant Perinatal Emergency Retrieval (PIPER) Service: 1300 137 650.
Discharge Criteria
Normal GCS
Normal ECG
Period of observation as above
For deliberate ingestion a risk assessment should indicate that the patient is at low risk of further self-harm in the discharge setting
Discharge information and follow-up
Poisoning
prevention for children Parent
information
Victorian Poisons Information Centre: 13 11 26 www.austin.org.au/poisons
Intentional self –harm: Referral to local mental health services eg Orygen Youth Health: 1800 888 320
Recreational poisoning: Referral to YoDAA, Victoria's Youth Drug and Alcohol Advice service: 1800 458 685
Last updated January 2018