warnings and cautions
5 WARNINGS AND PRECAUTIONS • Hypersensitivity Reactions : Hypersensitivity reactions, including anaphylaxis and bronchospasm have been reported in patients who have exhibited hypersensitivity to other selective 5-HT 3 receptor antagonists. ( 5.1 ) • QT Prolongation and Torsade de Pointes : QT prolongation occurs in a dose-dependent manner. Cases of Torsade de Pointes have been reported. Avoid ondansetron injection in patients with congenital long QT syndrome. ( 5.2 ) • Serotonin Syndrome : Serotonin syndrome has been reported with 5-HT 3 receptor agonists alone but particularly with concomitant use of serotonergic drugs. ( 5.3 ) • Masking of Progressive Ileus and/or Gastric Distention Following Abdominal Surgery or Chemotherapy-Induced Nausea and Vomiting : Monitor for decreased bowel activity, particularly in patients with risk factors for gastrointestinal obstruction. ( 5.4 ) 5.1 Hypersensitivity Reactions Hypersensitivity reactions, including anaphylaxis and bronchospasm, have been reported in patients who have exhibited hypersensitivity to other selective 5-HT 3 receptor antagonists. 5.2 QT Prolongation Ondansetron prolongs the QT interval in a dose-dependent manner [see Clinical Pharmacology (12.2) ] . In addition, postmarketing cases of Torsade de Pointes have been reported in patients using ondansetron. Avoid ondansetron injection in patients with congenital long QT syndrome. Electrocardiogram (ECG) monitoring is recommended in patients with electrolyte abnormalities (e.g., hypokalemia or hypomagnesemia), congestive heart failure, bradyarrhythmias, or patients taking other medicinal products that lead to QT prolongation. 5.3 Serotonin Syndrome The development of serotonin syndrome has been reported with 5-HT 3 receptor antagonists. Most reports have been associated with concomitant use of serotonergic drugs (e.g., selective serotonin reuptake inhibitors (SSRIs), serotonin and norepinephrine reuptake inhibitors (SNRIs), monoamine oxidase inhibitors, mirtazapine, fentanyl, lithium, tramadol, and intravenous methylene blue). Some of the reported cases were fatal. Serotonin syndrome occurring with overdose of ondansetron alone has also been reported. The majority of reports of serotonin syndrome related to 5-HT 3 receptor antagonist use occurred in a post-anesthesia care unit or an infusion center. Symptoms associated with serotonin syndrome may include the following combination of signs and symptoms: mental status changes (e.g., agitation, hallucinations, delirium, and coma), autonomic instability (e.g., tachycardia, labile blood pressure, dizziness, diaphoresis, flushing, hyperthermia), neuromuscular symptoms (e.g., tremor, rigidity, myoclonus, hyperreflexia, incoordination), seizures, with or without gastrointestinal symptoms (e.g., nausea, vomiting, diarrhea). Patients should be monitored for the emergence of serotonin syndrome, especially with concomitant use of ondansetron injection and other serotonergic drugs. If symptoms of serotonin syndrome occur, discontinue ondansetron injection and initiate supportive treatment. Patients should be informed of the increased risk of serotonin syndrome, especially if ondansetron injection is used concomitantly with other serotonergic drugs [see Drug Interactions (7.5) , Overdosage (10) ]. 5.4 Masking of Progressive Ileus and Gastric Distension The use of ondansetron injection in patients following abdominal surgery or in patients with chemotherapy-induced nausea and vomiting may mask a progressive ileus and gastric distention. Monitor for decreased bowel activity, particularly in patients with risk factors for gastrointestinal obstruction. Ondansetron injection is not a drug that stimulates gastric or intestinal peristalsis. It should not be used instead of nasogastric suction.