Dextromethorphan intoxication

8 Sep

Dextromethorphan (DXM):

Metabolism:

Hepatic P450 enzymes into active metabolite dextrorphan.  10% of patients are poor metabolizers.

Time of peak serum concentration is 2-2.5 hours

Half-life for DXM is 1.5-4 hrs.  Half-life for dextrorphan is 3-6 hrs


Receptor activity

  • DXM is an opioid agonist at the brain stem cough center. Can cause respiratory depression, particularly in children
  • Dextrorphan
    1. serotonergic agonist: can cause serotonin syndrome
    2. adrenergic reuptake inhibitor: tachycardia, mydriasis, HTN, diaphoresis
    3. NMDA and glutamate antagonist: behavioral effects ranging from euphoria to complete dissociation. Gait ataxia.

 

Clinical effects are at plateaus of DXM doses.

  • Mild stimulation at 1.5 mg/kg or 100-200 mg
  • Euphoria and hallucination at 2.5-7.5 mg/kg or 200-400 mg
  • Partial dissociation at 7.5 mg-15 mg/kg or 300-600 mg
  • Complete dissociation at 15 mg/kg or >600 mg

 

Formulations are often combination medications with:  

  • diphenhydramine,
  • acetaminophen,
  • salicylates,
  • phenylephrine,
  • and pseudoephedrine.

robo

Workup should include labs looking for coingestants like acetaminophen and salicylates. DXM levels are available only at dedicated toxicology laboratories and not helpful.

Treatment of respiratory depression is naloxone IV 0.1mg/kg.  Other than that, treatment is supportive and specific to coingestants.

 

Submitted by Matthew Kongkatong MD.

 

References:

Dextromethorphan. DrugPoints summary. Micromedex 2.0. Truven Health Analytics, Inc. Greenwood Village, CO. Available at: http://www.micromedexsolutions.com. Accessed September 4, 2014.

Rosenbaum Chris and Edward Boyer. Dextromethorphan abuse and poisoning: clinical features and diagnosis. In: UpToDate, Post TW (Ed), UpToDate, Waltham, MA.

Rosenbaum Chris and Edward Boyer. Dextromethorphan poisoning: treatment. In: UpToDate, Post TW (Ed), UpToDate, Waltham, MA.

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