Major
Established
Description
Escitalopram and ondansetron together carry dual risks: serotonin syndrome and additive QT interval prolongation, making this combination particularly dangerous.
Mechanism
Escitalopram inhibits SERT and prolongs the cardiac QT interval in a dose-dependent manner; ondansetron (5-HT3 antagonist) also prolongs QT and shares serotonergic receptor modulation.
Clinical Significance
FDA issued a drug safety communication (2011) specifically warning against high-dose escitalopram + ondansetron due to fatal arrhythmia risk.
Management
Avoid combining when possible; if essential, use the lowest effective doses, obtain baseline and follow-up ECGs, and correct electrolyte abnormalities.