What is the management for a patient with suspected dextromethorphan overdose, presenting with mydriasis (dilated pupils) and no other substances detected?

Management of Dextromethorphan Overdose with Mydriasis

For a patient presenting with dextromethorphan overdose (600mg) and mydriasis, prioritize airway protection and supportive care with continuous monitoring, as there is no specific antidote and management is entirely supportive. 1, 2

Immediate Stabilization

• Assess and secure the airway immediately – dextromethorphan overdose can cause altered mental status requiring intubation for airway protection, particularly at doses exceeding 70 mg/kg 3
• Provide rescue breathing or bag-mask ventilation if respiratory depression develops, maintaining ventilation until spontaneous breathing returns 4, 1
• Activate emergency response systems without delay 4, 1
• Monitor vital signs continuously, as dextromethorphan toxicity can cause tachycardia, hypertension, and hyperthermia 3, 5

Clinical Presentation to Anticipate

The 600mg dose represents a significant overdose (therapeutic doses are typically 10-30mg). Expected findings include:

• Neurological effects: Altered consciousness (potentially requiring intubation), mydriasis (which you've already observed), nystagmus, muscle rigidity, and potentially seizures 3, 5
• Cardiovascular effects: Tachycardia and hypertension are common 3
• Serotonin syndrome risk: Dextromethorphan can cause severe serotonin syndrome with hyperthermia, muscle rigidity, and autonomic instability 4, 5

Specific Management Steps

Decontamination

• Administer activated charcoal if the patient presents within 1-2 hours of ingestion and can protect their airway (or is intubated) 5
• Do not give activated charcoal if the patient cannot protect their airway or is having seizures 1

Supportive Care

• Benzodiazepines (midazolam or lorazepam) for agitation, muscle rigidity, or seizures – this is the primary pharmacologic intervention 4, 5
• Active cooling measures if hyperthermia develops (body surface cooling, cool IV fluids) 5
• IV fluids for hydration and to prevent rhabdomyolysis if muscle rigidity is present 4

Monitoring Parameters

• Serial neurological assessments including pupil size, mental status, and muscle tone 3, 5
• Continuous cardiac monitoring for dysrhythmias 4
• Core temperature monitoring 4, 5
• Consider checking creatine kinase if muscle rigidity is present (risk of rhabdomyolysis) 4
• Blood dextromethorphan levels can be obtained but do not guide acute management; levels >100 ng/mL are associated with toxicity in pediatric patients 3

Critical Pitfall to Avoid

Do NOT administer naloxone – dextromethorphan is not an opioid agonist despite its structural similarity to opioids, and naloxone will be ineffective 4, 2. The mydriasis (dilated pupils) is a key distinguishing feature, as opioid toxicity causes miosis (pinpoint pupils) 4.

Serotonin Syndrome Considerations

If the patient develops the triad of hyperthermia, muscle rigidity, and altered mental status:

• Administer cyproheptadine (serotonin antagonist): 12 mg initial dose, then 2 mg every 2 hours for continuing symptoms, with maintenance of 8 mg every 6 hours orally or via nasogastric tube 4
• Aggressive cooling and benzodiazepines remain the mainstay 4, 5
• In severe refractory cases, intravenous lipid emulsion has been reported as a rescue therapy, though evidence is limited to case reports 5

Disposition and Observation

• Observe for at least 12-24 hours given the potential for prolonged effects, particularly if an extended-release formulation was ingested 3
• The patient can be discharged once mental status normalizes, vital signs stabilize, and mydriasis resolves 3, 5
• Contact Poison Control (1-800-222-1222) for additional guidance 1, 6