Dextromethorphan toxicity
The case
A 19-year-old man is brought in by ambulance for acute altered mental status (my favorite chief complaint!). The paramedics state his parents called 911 when they noticed their son appeared agitated and his eyes were moving rapidly back and forth. They also found multiple empty boxes of an over-the-counter cough medication in his bedroom. The boxes contained a total of 30 tablets. His parents report a history of depression, but state he had stopped taking his medication (sertraline) about 8 weeks ago.
The patient denies any acute complaints, but states he had an argument with his father earlier in the day, and subsequently took the cough medication to "feel better." He denies ingesting any other medication, alcohol, or illicit drug use. Before being transported to the ED, police had placed the patient on an involuntary psychiatric hold for danger to self.
Vital signs: T 99.6, HR 125, BP 140/80, RR 18, O2 sat 100% RA
On physical examination, the patient is awake. He is smiling and intermittently laughs inappropriately. He exhibits diaphoresis, mydriasis (sluggishly reactive to light), nystagmus (multiple directions), and "zombie-like" ataxia. He is oriented to person only. He follows simple commands appropriately. Speech is clear. He exhibits no external signs of trauma.
Laboratory evaluation reveals his urine drug screen is positive for phencyclidine (PCP). EKG demonstrates sinus tachycardia with no other acute abnormalities.
His parents arrive later and bring the empty boxes of Coricidin HBP Cough & Cold (chlorpheniramine/dextromethorphan) they suspect he ingested. No other medications or drug paraphernalia were found in the house.
The brush up
Dextromethorphan (DXM) is structurally similar to an opioid, though its mechanism of action is most similar to codeine (antitussive). It does not typically produce an opioid-like toxidrome as it does not act at mu or kappa opioid receptors.
DXM is metabolized to its active metabolite, dextrorphan, which appears to be mostly responsible for the psychoactive effects. Both act as NMDA receptor antagonists (responsible for the dissociative effects similar to ketamine and PCP) as well as serotonin reuptake inhibition (euphoria, hallucinations, among other effects).
As an over-the-counter medication, DXM has been around since the 1950s. It made its debut as a cough syrup named Romilar, but was later taken off the market due to recreational abuse. The preparation was subsequently remarketed as a bad-tasting liquid to divert abuse (and it actually took a large volume ingestion to experience any psychoactive effects). Today, DXM can be found in multiple products including Robitussin, Delsym, Nyquil, and Dimetapp. Coricidin HBP (dextromethorphan HBr) products were developed as an alternative for patients with hypertension because they do not contain phenylephrine or pseudoephedrine found in other over-the-counter preparations (but most contain acetaminophen and/or an antihistamine, so consider toxicity from these as well). Some (serious) DXM abuses will even try to extract the free base (known as "crystal dex") to minimize effects from other ingredients.
Due to molecular similarity, DXM can result in a false positive PCP assay on standard urine drug screening.
The usual management of DXM toxicity is, as you might have guessed, supportive. There is no specific antidote for DXM itself. Gastric decontamination with activated charcoal is appropriate for ingestions within 1-2 hours of presentation, as long as the patient can cooperate. Benzodiazepines will likely be effective for hyperthermia, severe agitation, and seizures. Because of its relatively large volume of distribution, DXM is not amenable to enhanced elimination (e.g. hemodialysis). Patients with mild toxicity can usually be observed for about 6 hours and discharged if improving.
The resolution
After observing the patient in the ED for 6 hours, his mental status and vital signs normalized. He was medically cleared for transfer to a psychiatric facility. Before transfer, the patient called me into the room and gave me some paper crafts he made while he was in the ED (not sure how this got by security...)
I don't know how he knew I liked origami. I kept them, of course. :)
References
1. Olson KR & California Poison Control System. (2012). Poisoning & drug overdose. New York: Lange Medical Books/McGraw-Hill.
2. Rosenbaum C, Boyer EW. Dextromethorphan abuse and poisoning: Clinical features and diagnosis. In: UpToDate, Wiley JF (Ed), UpToDate, Waltham, MA, 2015.
3. Rosenbaum C, Boyer EW. Dextromethorphan poisoning: Treatment. In: UpToDate, Wiley JF (Ed), UpToDate, Waltham, MA, 2015.