When dogs ingest more than one type of antidepressant medication, the likelihood of serotonin syndrome increases. The syndrome most commonly occurs when two or more serotonergic agents with different mechanisms of action are ingested either concurrently or in close succession, leading to excessive serotonin concentrations in the central nervous system. Other drugs such as 5-hydroxytryptophan, dextromethorphan hydrobromide, and lithium act synergistically with TCAs, MAOIs, SSRIs, and novel antidepressants and can lead to serotonin syndrome. Because of the severity of the signs, serotonin syndrome is much more difficult to treat than a simple overdose. Signs generally resolve over 12 to 24 hours, but you must closely monitor affected dogs.
Treatment is symptomatic and supportive.
You can use activated charcoal, but the risk of aspiration needs to be considered in a vomiting patient or one with neurologic signs. Seizures often abate with diazepam or barbiturate therapy. Metabolic acidosis may occur and can be treated with sodium bicarbonate as indicated by blood gas analysis. Although there are no controlled studies, cyproheptadine may be given rectally at the same dose. Conclusion Overdoses of SSRIs have fewer cardiac effects and are much less likely to be fatal than overdoses of TCAs or MAOIs.