Serotonin syndrome

A 55-year-old woman comes to the emergency department (ED) for evaluation of recurrent left flank pain and vomiting. She has a history of recurrent nephrolithiasis and recently noticed gross blood in her urine. Medical history is notable for obesity, hypertension, hyperlipidemia, depression, and type II diabetes mellitus. The patient has been taking ondansetron at home for nausea as well as losartan, metformin, rosuvastatin, and sertraline for her other medical conditions. On physical exam, the patient has left costovertebral angle tenderness. Blood is detected on urinalysis. The patient's symptoms are well controlled during the ED visit, and she is subsequently discharged with prescription analgesia, additional antiemetics, and urology follow-up. Three days later, the patient is brought back to the ED altered, diaphoretic, and agitated. Temperature is 39.4°C (103°F), pulse is 122/min, respirations are 20/min, and blood pressure is 184/95 mmHg. She has bilateral mydriasis and myoclonus. Which of the following medications was the most likely precipitant of this patient's clinical presentation?