Drug Interactions between Zofran ODT and Zoloft

MONITOR CLOSELY: Concomitant use of 5-HT3 receptor antagonists with agents that possess or enhance serotonergic activity such as selective serotonin reuptake inhibitors (SSRIs) may potentiate the risk of serotonin syndrome, which is a rare but serious and potentially fatal condition thought to result from hyperstimulation of brainstem 5-HT1A and 2A receptors. According to the manufacturers, development of serotonin syndrome has been reported with 5-HT3 receptor antagonists, primarily during concomitant use of serotonergic drugs but also in overdose. Some of the reported cases were fatal. Symptoms of the serotonin syndrome may include mental status changes such as irritability, altered consciousness, confusion, hallucination, and coma; autonomic dysfunction such as tachycardia, hyperthermia, diaphoresis, shivering, blood pressure lability, and mydriasis; neuromuscular abnormalities such as hyperreflexia, myoclonus, tremor, rigidity, and ataxia; and gastrointestinal symptoms such as abdominal cramping, nausea, vomiting, and diarrhea.

MONITOR CLOSELY: Treatment with 5-HT3 receptor antagonists has been associated with dose-dependent prolongation of the QT interval. Theoretically, coadministration with other agents that can prolong the QT interval including some SSRIs may result in additive effects and increased risk of ventricular arrhythmias such as torsade de pointes and sudden death. Cases of torsade de pointes have been specifically reported with dolasetron and ondansetron during postmarketing use. It is uncertain whether palonosetron also causes significant prolongation of the QT interval. A thorough QT/QTc study in healthy volunteers demonstrated no relevant effect on QT/QTc interval duration or any other ECG interval at doses up to 2.25 mg. However, non-clinical studies have shown that palonosetron possesses the ability to block ion channels involved in ventricular de- and re-polarization and to prolong action potential duration. In general, the risk of an individual agent or a combination of agents causing ventricular arrhythmia in association with QT prolongation is largely unpredictable but may be increased by certain underlying risk factors such as congenital long QT syndrome, cardiac disease, and electrolyte disturbances (e.g., hypokalemia, hypomagnesemia). Also, the extent of drug-induced QT prolongation is dependent on the particular drug(s) involved and dosage(s) of the drug(s).

Limited data suggest that SSRIs and 5-HT3 receptor antagonists may demonstrate mutual antagonism due to opposing pharmacologic effects involving serotonin. In one report, three patients receiving carboplatin-containing chemotherapy had inadequate antiemetic response to ondansetron while they were taking fluoxetine. Ondansetron efficacy improved after fluoxetine was discontinued. Another case report describes the occurrence of a brief episode of depressive symptoms following the initiation of ondansetron treatment in a woman whose depression had been under control with fluoxetine.

MANAGEMENT: Caution is advised if 5-HT3 receptor antagonists are prescribed in combination with SSRIs. Patients should be closely monitored for symptoms of the serotonin syndrome during treatment. Particular caution is warranted when initiating or increasing the dosages of these agents. The potential risk for serotonin syndrome should be considered even when administering serotonergic agents sequentially, as some agents may demonstrate a prolonged elimination half-life. For example, a 5-week washout period is typically recommended following use of fluoxetine before administering another serotonergic agent. If serotonin syndrome develops or is suspected during the course of therapy, all serotonergic agents should be discontinued immediately and supportive care rendered as necessary. Moderately ill patients may also benefit from the administration of a serotonin antagonist (e.g., cyproheptadine, chlorpromazine). Severe cases should be managed under consultation with a toxicologist and may require sedation, neuromuscular paralysis, intubation, and mechanical ventilation in addition to the other measures.

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