What are common contraindications to ondansetron?

• A. Known hypersensitivity to ondansetron
• B. QT prolongation risks in susceptible patients
• C. Both of the above
• D. None of the above

Answer: (B)

Ondansetron safety hinges on avoiding effects that can affect the heart’s rhythm. The main concept here is that this drug can prolong the QT interval, which in turn can lead to dangerous arrhythmias like torsades de pointes in patients who are susceptible. This makes QT prolongation a common and important contraindication to use of ondansetron.

In susceptible individuals—such as those with congenital long QT syndrome, electrolyte disturbances (low potassium or magnesium), bradycardia, or those taking other drugs that prolong the QT interval—the risk is higher. Because of this broad risk across many patients and situations, avoiding ondansetron in these scenarios is a key safety consideration.

It’s true that known hypersensitivity to ondansetron is also a contraindication, but the choice emphasized here focuses on the more widely applicable reason to avoid use in routine practice: QT prolongation risk in susceptible patients. When such risk factors are present, alternative antiemetics are typically chosen.