Fast Five Quiz: Do You Know About Newer Drugs of Abuse?

Mary L. Windle, PharmD


August 11, 2016

Dextromethorphan is a synthetic opioid that acts at opiate receptors in the central nervous system, but whose effects differ from many of those of typical opiates: It has minimal analgesic and minimal tolerance properties. Its mechanism of action is that of a weak N-methyl-D-aspartate (NMDA) receptor antagonist. Ketamine is a potent NMDA antagonist.

NMDA is a receptor for the excitatory neurotransmitter glutamate, which is released with noxious peripheral stimuli. Activation of NMDA receptors has been associated with hyperalgesia; neuropathic pain; and reduced functionality of opioid receptors, which results in decreased opioid receptor sensitivity and emergence of tolerance. NMDA antagonists elicit varying degrees of analgesia with minimal or no tolerance.

Dilated and minimally reactive pupils have been seen with antihistamine toxicity related to anticholinergic effects. Mydriasis and nystagmus may be observed with dextromethorphan ingestion. If the patient has ingested less than 10 mg/kg of dextromethorphan, he or she can be treated at home. If the patient has ingested a long-acting dextromethorphan, refer him or her to a healthcare facility for evaluation.

Drug interactions between dextromethorphan and MAOIs or serotonin reuptake inhibitors may result in a serotonin syndrome, which consists of the following:

  • Mental status changes (eg, agitation)

  • Myoclonus

  • Hyperreflexia

  • Diaphoresis

  • Shivering

  • Tremor

  • Diarrhea

  • Headache

  • Fever

  • Incoordination

For more cough, cold, and allergy preparation toxicity, read here.

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