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Dextromethorphan Clinical Pearls

In this article, we’d like to share some of the most common dextromethorphan clinical pearls that you should be aware of. Dextromethorphan (DXM) is an over-the-counter medication often found in many of the Robitussin products, among others.  It is approved to treat cough in adults and children 12 and older.  Relief starts 15-30 minutes after taking dextromethorphan and should last for 5-6 hours after each dose.  Usual adult dosing is 30 mg by mouth every 6 to 8 hours, with a maximum of 120 mg per day.  There are no dose adjustments necessary for geriatric patients, or patients with renal or hepatic dysfunction.  Dextromethorphan is generally well-tolerated – some patients may experience mild dizziness or tiredness at standard dosages.  

Dextromethorphan should not be taken within 14 days of a monoamine oxidase inhibitor (MAOI).  Patients with chronic or persistent cough from an underlying condition such as asthma, emphysema, or smoking should not use dextromethorphan, nor should patients with an excessively productive cough.  If a cough is accompanied by fever, rash, or persistent headache, the patient should discontinue dextromethorphan and consult a physician.  Patients should also discontinue dextromethorphan and consult a physician if their cough returns or lasts longer than 7 days. If you work at a pharmacy and notice patients going to purchase dextromethorphan, it is a great opportunity to intervene and ensure that the cough is not medication-related or that the patient should be referred for a clinical assessment by a trained medical provider.

Dextromethorphan is primarily metabolized by CYP2D6 and CYP3A4.  CYP2D6 metabolizes dextromethorphan to the active metabolite dextrorphan. There are potential interactions to be aware of.  Dextromethorphan may interact with drugs that inhibit CYP2D6 (such as fluoxetine or paroxetine), resulting in an increased concentration of dextromethorphan.  Serotonergic drugs such as SNRIs, SSRIs, and tramadol can result in an increased risk of serotonin syndrome when taken with dextromethorphan. In patients who are taking multiple serotonergic drugs or higher dosages of serotonergic drugs, we may have to watch this risk a little more closely.

Dextromethorphan carries the potential for abuse.  At high doses, it is considered a hallucinogenic drug with dissociative properties.  The active metabolite dextrorphan is an NMDA agonist akin to PCP or ketamine, and it inhibits catecholamine reuptake centrally and peripherally.  At high doses, dextromethorphan can interact with opioid receptors and may resemble opioid toxicity (respiratory depression or miosis).  There is also a risk for other toxicities when a combination product is abused.  For example, some dextromethorphan products also contain acetaminophen, which leads to a concern for hepatotoxicity if the product is abused. 

Hopefully these dextromethorphan clinical pearls help you take better care of your patients! This article was written by Sarah Jackson PharmD Candidate in collaboration with Eric Christianson, PharmD, BCPS, BCGP.

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