Organic psychosis and nystagmus? consider dextromethorphan toxicity

September 25, 2017, 9:46 pm

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Dextromethorphan in Cough Syrup: The Poor Man’s Psychosis. Martinak B et al. Psychopharmacol Bull 2017 Sep 15:47:59-63.

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Dextromethorphan (DXM) is found in many over-the-counter cough and cold medications. At recommended therapeutic dosage (up to 120 mg per day in divided doses) DXM is safe and has no psychiatric effects. However, DXM and its major metabolite —dextrorphan — act as NMDA receptor antagonists, producing effects similar to those of phencyclidine (PCP) or ketamine when taken in large amounts.

The intensity of psychiatric symptoms seen after DXM overdose is dose-dependent. ranging from alterations in perception as well as motor and cognitive function to agitation, violent behavior, and hyperthermia. Management of these patients focuses on suppportive care and administration of benzodiazepine and antipsychotic medication.

This case report describes a 40-year-old woman with a long history of psychotic presentations associated with abuse of various drugs such as LSD, amphetamine, and marijuana. She had been abusing DXM for years. In this instance, she was brought to hospital after assaulting a police officer. She was described as irritable, hostile and suspicious, with labile mood and disorganized thought processes.

This case report is not quite as convincing as others that have been reported previously (see here and here) because of the patient’s long history of DXM abuse, and the somewhat vague clinical description of her presentation.  However, it does remind us that DXM toxicity should be in the differential diagnosis when a patient presents with new-onset and otherwise unexplained psychosis. Although the authors don’t mention it, one clue to the diagnosis might be the presence of nystagmus. One other take-home lesson is that DXM will not itself show up on a urine drug screen, but in large amounts can produce a false-positive urine screen for PCP.

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