Two Cases of Serotonin Syndrome with Venlafaxine and Calcineurin Inhibitors

Serotonin syndrome is a potentially life-threatening condition described in all age groups. The diagnosis is clinically determined by either the Sternbach or the Hunter criteria. These criteria are based on recent serotonergic agent use and physical examination findings, including tremor, hyperreflexia, myoclonus, muscle rigidity, diaphoresis, nystagmus, or hyperthermia. The syndrome is an adverse reaction in which a drug is used alone or in combination with another drug resulting in increased centrally available serotonin. One such drug that has been shown to cause serotonin syndrome is the serotonergic-noradrenergic receptor reuptake inhibitor (SNRI) venlafaxine, which is commonly used for major depressive disorder (MDD). We report in this article serotonin syndrome caused by the combination of venlafaxine with a calcineurin inhibitor in two cases of transplant patients diagnosed with MDD. One patient was immunosuppressed with tacrolimus while the other was immunosuppressed with cyclosporine.