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PRECAUTIONS: Before using ondansetron, tell your doctor or pharmacist if you are allergic to it; or to other serotonin blockers (e.g., granisetron); or if you have any other allergies.Before using this medication, tell your doctor or pharmacist your medical history, especially of: irregular heartbeat, liver disease, stomach/intestinal problems (e.g., recent abdominal surgery, ileus, swelling).Ondansetron may cause a condition that affects the heart rhythm (QT prolongation). QT prolongation can infrequently result in serious (rarely fatal) fast/irregular heartbeat and other symptoms (such as severe dizziness, fainting) that require immediate medical attention. The risk of QT prolongation may be increased if you have certain medical conditions or are taking other drugs that may affect the heart rhythm (see also Drug Interactions section). Before using ondansetron, tell your doctor or pharmacist if you have any of the following conditions: certain heart problems (heart failure, slow heartbeat, QT prolongation in the EKG), family history of certain heart problems (QT prolongation in the EKG, sudden cardiac death).Low levels of potassium or magnesium in the blood may also increase your risk of QT prolongation. This risk may increase if you use certain drugs (such as diuretics/"water pills") or if you have conditions such as severe sweating, diarrhea, or vomiting. Talk to your doctor about using ondansetron safely.This drug may make you dizzy or drowsy or cause blurred vision. Do not drive, use machinery, or do any activity that requires alertness or clear vision until you are sure you can perform such activities safely. Limit alcoholic beverages.During pregnancy, this medication should be used only when clearly needed. Discuss the risks and benefits with your doctor.It is not known if this drug passes into breast milk. Consult your doctor before breast-feeding.

DRUG INTERACTIONS: Your doctor or pharmacist may already be aware of any possible drug interactions and may be monitoring you for them. Do not start, stop, or change the dosage of any medicine before checking with them first.This drug should not be used with the following medication because a very serious interaction may occur: apomorphine.If you are currently using the medication listed above, tell your doctor or pharmacist before starting ondansetron.Before using this medication, tell your doctor or pharmacist of all prescription and nonprescription/herbal products you may use, especially: tramadol.Many drugs besides ondansetron may affect the heart rhythm (QT prolongation), including dofetilide, pimozide, procainamide, amiodarone, quinidine, sotalol, macrolide antibiotics (such as erythromycin), among others. Therefore, before using ondansetron, report all medications you are currently using to your doctor or pharmacist.This document does not contain all possible interactions. Therefore, before using this product, tell your doctor or pharmacist of all the products you use. Keep a list of all your medications with you, and share the list with your doctor and pharmacist.

Report Problems to the Food and Drug Administration   You are encouraged to report negative side effects of prescription drugs to the FDA. Visit the FDA MedWatch website or call 1-800-FDA-1088. Need help identifying pills and medications? Use the pill identifier tool on RxList.