Dextromethorphan is a non-addictive opioid that acts centrally by increasing the cough threshold, and is an ingredient that gets a lot of attention at the ASPCA Animal Poison Control Center during cold and flu season.
At high doses of ingestion, we can serotonin agonist activity. The most common signs are those associated with an allergic reaction to the dextromethorphan – urticaria and facial swelling. These signs can be treated the same as other allergic reactions with antihistamines and corticosteroids, if needed.
At low doses, we can see vomiting and lethargy. At very high doses, we can see agitation, tachycardia, tremors, and seizures.
In most cases, pets can be monitored at home. With pets who are showing more significant signs, treatment is largely symptomatic and supportive.
IV fluids can help with the excretion. Benzodiazepines are typically recommended for tremoring and seizing pets. Chlorpromazine, acepromazine, or cyproheptadine can be used for serotonin syndrome. Naloxone can be used to reverse significant CNS depression.