Before giving ondansetron, the nurse notes potassium 3.1 mEq/L and a concurrent methadone prescription. Which action should the nurse take?
1Administer ondansetron now and recheck the potassium with the next routine laboratory panel.
2Hold the dose, notify the prescriber, and anticipate electrolyte correction with ECG monitoring.✓ Correct answer
3Give ondansetron with a potassium-rich snack and omit cardiac rhythm assessment.
4Administer two doses together and monitor bowel sounds after the infusion is complete.
Explanation
Ondansetron can prolong the QT interval, and ECG monitoring is recommended when the client has hypokalemia or takes another QT-prolonging medication. Potassium 3.1 mEq/L plus methadone creates a modifiable torsades de pointes risk, so the nurse should hold the dose, notify the prescriber, and anticipate electrolyte correction and cardiac assessment. Food does not promptly correct this risk, and extra dosing can worsen QT prolongation.
Clinical reasoning Hypokalemia reduces repolarization reserve, while ondansetron and methadone can both prolong the QT interval. The combination increases the risk of a malignant ventricular rhythm.
Decision rule Correct potassium and magnesium abnormalities and review concurrent QT-prolonging drugs before administering ondansetron to a high-risk client.
Scenario 55-year-old female receiving chemotherapy; ondansetron 8 mg IV ordered for nausea. ECG: QTc 510 ms, K+ 3.3, also on methadone.
5-HT3 antagonist — An antiemetic class that blocks serotonin receptors; ondansetron is effective for nausea but can prolong the QT interval.
QT prolongation — Delayed ventricular repolarization that can progress to torsades de pointes, especially with electrolyte abnormalities or interacting drugs.
Drug-induced torsades — Polymorphic VT from QT-prolonging drugs; treated with IV magnesium.