Management of Tizanidine Overdose
The treatment of tizanidine overdose should focus on basic supportive care with emphasis on airway management, cardiovascular monitoring, and respiratory support, as there is no specific antidote for tizanidine toxicity. 1
Clinical Presentation
Tizanidine overdose typically presents with:
- Central nervous system depression: Somnolence, stupor, or coma
- Cardiovascular effects: Bradycardia and hypotension (due to α2-adrenergic agonist activity)
- Respiratory depression: May progress to respiratory failure
- Other symptoms: Confusion, agitation, vomiting
Management Algorithm
1. Initial Stabilization
- Secure airway: Intubation may be necessary in patients with significant CNS depression
- Establish IV access
- Continuous cardiac monitoring
- Frequent vital sign assessment
2. Cardiovascular Support
- Treat hypotension:
- IV fluid resuscitation as first line
- Vasopressors (norepinephrine preferred) for refractory hypotension 2
- Monitor for QT prolongation and arrhythmias
3. Gastrointestinal Decontamination
- Activated charcoal: Consider if patient presents within 1 hour of ingestion and has intact airway or is intubated
- Avoid induced emesis due to risk of rapid CNS depression
4. Monitoring and Supportive Care
- Electrolyte monitoring: Watch for hypokalemia which can be severe and refractory 3
- Renal function monitoring: Tizanidine overdose has been associated with acute kidney injury 3
- Liver function monitoring: Cases of hepatic dysfunction have been reported, particularly in pediatric overdoses 4
- Temperature regulation: Monitor for hypothermia
5. Special Considerations
- Duration of monitoring: Symptoms typically resolve within 1-3 days following discontinuation of tizanidine 1
- Contact Poison Control Center: For the most recent information concerning management of overdose 1
Important Clinical Pearls
- The mechanism of action of tizanidine is similar to clonidine, and management approaches are comparable 1
- Naloxone has been used in tizanidine overdose but has shown inconsistent results; in a retrospective review, only 1 of 7 patients showed arousal response to naloxone 5
- Pediatric patients may be particularly vulnerable to tizanidine toxicity, with reports of liver, renal, and cardiovascular failure even at relatively low doses 4
Potential Complications to Monitor
- Cardiac: Prolonged myocardial dysfunction has been reported, with complete recovery potentially taking up to one year 2
- Metabolic: Potassium wasting nephropathy causing severe hypokalemia that may be refractory to replacement 3
- Neurological: Seizures have been reported in severe cases
Prognosis
With appropriate supportive care, most patients recover completely from tizanidine overdose. In a retrospective review of 45 cases, all patients recovered without residual complications with supportive therapy 5. However, vigilance for potential complications is essential, particularly in cases involving co-ingestion with other CNS depressants, which have been associated with increased mortality 1.