Before you begin using a medication, be sure to inform your doctor of any medical conditions or Allergies you may have, any medications you are taking, whether you are pregnant or breast-feeding, and any other significant facts about your health. These factors may affect how you should use Ondansetron.

Allergy: People who have had an allergic reaction to Dolasetron or Granisetron are advised not to take ondansetron. Before you take ondansetron, inform your doctor about any previous adverse reactions you have had to medications. Contact your doctor at once if you experience signs of an allergic reaction such as skin rash, itching, difficulty breathing, or swelling of the face and throat.

Abnormal heart rhythms: Very rarely, ondansetron can affect the heart's electrical activity and cause an irregular heartbeat. This is more likely to happen with the injectable form of ondansetron. Certain medications (e.g., Sotalol, quinidine, thioridazine, Chlorpromazine, Pimozide, moxifloxacin, Mefloquine, pentamidine, arsenic trioxide, probucol, Tacrolimus) can increase the risk of a type of abnormal heart rhythm called QT prolongation, and should not be used in combination with ondansetron. You are more at risk for this type of abnormal heart rhythm and its complications if you:

• are female
• are older than 65 years of age
• have a family history of sudden cardiac death
• have a history of heart disease or abnormal heart rhythms
• have a slow heart rate
• have congenital prolongation of the QT interval
• have Diabetes
• have had a Stroke
• have low potassium, magnesium, or calcium levels
• have nutritional deficiencies

If you have heart disease and abnormal heart rhythms, or are taking certain medications (e.g., Verapamil, atazanavir), discuss with your doctor how Ondansetron may affect your medical condition, how your medical condition may affect the dosing and effectiveness of Ondansetron, and whether any special monitoring is needed. Your doctor may monitor your heart rate using a test called an electrocardiogram (ECG) while you are using Ondansetron.

Liver function: Ondansetron is broken down and removed from the body by the liver. Decreased liver function slows down the removal of the medication from the body and increases the risk of side effects from ondansetron. If you have liver disease or reduced liver function, discuss with your doctor how Ondansetron may affect your medical condition, how your medical condition may affect the dosing and effectiveness of Ondansetron, and whether any special monitoring is needed.

Motion Sickness: Ondansetron is not effective for the treatment of motion sickness.

Neuroleptic malignant syndrome (NMS): Ondansetron, like other similar medications, can cause a potentially fatal syndrome known as neuroleptic malignant syndrome (NMS). If you notice the symptoms of NMS such as high fever, muscle stiffness, confusion or loss of consciousness, sweating, racing or irregular heartbeat, or fainting, get immediate medical attention.

Phenylketonuria: People with phenylketonuria (lacking the enzyme needed to break down phenylalanine) should take forms of ondansetron other than oral dissolving tablets (ODT). The ODT form of ondansetron contains aspartame, an ingredient that cannot be broken down in the body by people who have phenylketonuria.

Serotonin syndrome: Severe reactions are possible when ondansetron is combined with other medications that act on serotonin, such as tricyclic antidepressants and serotonin reuptake inhibitors, medications used to treat Depression. These combinations must be avoided. Symptoms of a reaction may include muscle rigidity and spasms, difficulty moving, and changes in mental state including delirium and agitation. Coma and death are possible.

Pregnancy: The safety of ondansetron for use by pregnant women has not been established. Ondansetron should not be used during pregnancy unless the benefits outweigh the risks. If you become pregnant while taking Ondansetron, contact your doctor immediately.

Breast-feeding: It is not known if ondansetron passes into breast milk. If you are a breast-feeding mother and are taking Ondansetron, it may affect your baby. Talk to your doctor about whether you should continue breast-feeding.

Children: The safety and effectiveness of using Ondansetron to treat nausea and vomiting caused by chemotherapy have not been established for children under 3 years of age. The safety and effectiveness of using Ondansetron to treat nausea and vomiting caused by radiation or surgery have not been determined for children less than 18 years of age. Its use by this age group is not recommended.

Seniors: The safety and effectiveness of using Ondansetron by people 65 years or older to treat nausea and vomiting caused by surgery have not been established. Seniors may be at an increased risk of developing irregular heart beat with ondansetron, particularly the injectable form. Talk to your doctor about any concerns you may have.