ONDANSETRON Drug Interactions: What You Need to Know

INTERACTIONS

7.1 Drugs Affecting Cytochrome P-450 Enzymes Ondansetron does not appear to induce or inhibit the cytochrome P-450 drug-metabolizing enzyme system of the liver. Because ondansetron is metabolized by hepatic cytochrome P-450 drug-metabolizing enzymes (CYP3A4, CYP2D6, CYP1A2), inducers or inhibitors of these enzymes may change the clearance and, hence, the half-life of ondansetron <span class="opacity-50 text-xs">[see Clinical Pharmacology (12.3) ]</span> . On the basis of limited available data, no dosage adjustment is recommended for patients on these drugs.

7.2 Apomorphine Based on reports of profound hypotension and loss of consciousness when apomorphine was administered with ondansetron, the concomitant use of apomorphine with ondansetron is contraindicated <span class="opacity-50 text-xs">[see Contraindications (4) ]</span>.

7.3 Phenytoin, Carbamazepine, and Rifampin In patients treated with potent inducers of CYP3A4 (i.e., phenytoin, carbamazepine, and rifampin), the clearance of ondansetron was significantly increased and ondansetron blood concentrations were decreased. However, on the basis of available data, no dosage adjustment for ondansetron is recommended for patients on these drugs <span class="opacity-50 text-xs">[see Clinical Pharmacology (12.3) ]</span> .

7.4 Tramadol Although there are no data on pharmacokinetic drug interactions between ondansetron and tramadol, data from two small trials indicate that concomitant use of ondansetron may result in reduced analgesic activity of tramadol. Patients on concomitant ondansetron self administered tramadol more frequently in these trials, leading to an increased cumulative dose in patient-controlled administration (PCA) of tramadol.

7.5 Serotonergic Drugs Serotonin syndrome (including altered mental status, autonomic instability, and neuromuscular symptoms) has been described following the concomitant use of 5-HT 3 receptor antagonists and other serotonergic drugs, including selective serotonin reuptake inhibitors (SSRIs) and serotonin and noradrenaline reuptake inhibitors (SNRIs) <span class="opacity-50 text-xs">[see Warnings and Precautions (5.3) ]</span> .

7.6 Chemotherapy In humans, carmustine, etoposide, and cisplatin do not affect the pharmacokinetics of ondansetron. In a crossover trial in 76 pediatric patients, intravenous ondansetron did not increase blood levels of high-dose methotrexate.

7.7 Temazepam The coadministration of ondansetron had no effect on the pharmacokinetics and pharmacodynamics of temazepam.

7.8 Alfentanil and Atracurium Ondansetron does not alter the respiratory depressant effects produced by alfentanil or the degree of neuromuscular blockade produced by atracurium. Interactions with general or local anesthetics have not been studied.

7.5 Serotonergic Drugs Serotonin syndrome (including altered mental status, autonomic instability, and neuromuscular symptoms) has been described following the concomitant use of 5-HT 3 receptor antagonists and other serotonergic drugs, including selective serotonin reuptake inhibitors (SSRIs) and serotonin and noradrenaline reuptake inhibitors (SNRIs) <span class="opacity-50 text-xs">[see Warnings and Precautions (5.3) ]</span> .

Ondansetron Injection, USP is contraindicated for patients known to have hypersensitivity (e.g., anaphylaxis) to this product or any of its components. Anaphylactic reactions have been reported in patients taking ondansetron. [ See Adverse Reactions (6.2) ]. The concomitant use of apomorphine with ondansetron is contraindicated based on reports of profound hypotension and loss of consciousness when apomorphine was administered with ondansetron. Patients known to have hypersensitivity (e.g., anaphylaxis) to this product or any of its components. ( 4 ) Concomitant use of apomorphine. ( 4 , 7.2 )

AND PRECAUTIONS

• Hypersensitivity Reactions, Including Anaphylaxis and Bronchospasm : Discontinue ondansetron if suspected. Monitor and treat promptly per standard of care until signs and symptoms resolve. ( 5.1 )
• QT Interval Prolongation and Torsade de Pointes : Avoid ondansetron in patients with congenital long QT syndrome; monitor with electrocardiograms (ECGs) if concomitant electrolyte abnormalities, cardiac failure or arrhythmias, or use of other QT prolonging drugs. ( 5.2 )
• Serotonin Syndrome : Reported with 5-HT 3 receptor antagonists alone but particularly with concomitant use of serotonergic drugs. If such symptoms occur, discontinue ondansetron and initiate supportive treatment. If concomitant use of ondansetron with other serotonergic drugs is clinically warranted, patients should be made aware of a potential increased risk for serotonin syndrome. ( 5.3 )
• Myocardial Ischemia : Monitor or advise patients for signs and symptoms of myocardial ischemia after oral administration. ( 5.4 )
• Masking of Progressive Ileus and/or Gastric Distension Following Abdominal Surgery or Chemotherapy-Induced Nausea and Vomiting : Monitor for decreased bowel activity, particularly in patients with risk factors for gastrointestinal obstruction. ( 5.5 )
• Phenylketonuria: Patients should be informed that ondansetron orally disintegrating tablets contain phenylalanine (a component of aspartame).

Each

4 mg orally disintegrating tablet contains 1.68 mg phenylalanine and 8 mg orally disintegrating tablet contains 3.37 mg phenylalanine. ( 5.6 )

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. If hypersensitivity reactions occur, discontinue use of ondansetron; treat promptly per standard of care and monitor until signs and symptoms resolve <span class="opacity-50 text-xs">[see Contraindications (4) ]</span> .

5.2 QT Prolongation Electrocardiogram (ECG) changes, including QT interval prolongation have been seen in patients receiving ondansetron. In addition, postmarketing cases of Torsade de Pointes have been reported in patients using ondansetron. Avoid ondansetron in patients with congenital long QT syndrome. 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 <span class="opacity-50 text-xs">[see Clinical Pharmacology (12.2) ]</span> .

5.3 Serotonin Syndrome The development of serotonin syndrome has been reported with 5-HT 3 receptor antagonists alone. 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 and other serotonergic drugs. If symptoms of serotonin syndrome occur, discontinue ondansetron and initiate supportive treatment. Patients should be informed of the increased risk of serotonin syndrome, especially if ondansetron is used concomitantly with other serotonergic drugs <span class="opacity-50 text-xs">[see Drug Interactions (7.1) , Overdosage (10) ]</span> .

5.4 Myocardial Ischemia Myocardial ischemia has been reported in patients treated with ondansetron. In some cases, predominantly during intravenous administration, the symptoms appeared immediately after administration but resolved with prompt treatment. Coronary artery spasm appears to be the most common underlying cause. Therefore, monitor or advise patients for signs or symptoms of myocardial ischemia after oral administration of ondansetron <span class="opacity-50 text-xs">[see Adverse Reactions (6.2) ]</span>.

5.5 Masking of Progressive Ileus and Gastric Distension The use of ondansetron in patients following abdominal surgery or in patients with chemotherapy-induced nausea and vomiting may mask a progressive ileus and/or gastric distension. Monitor for decreased bowel activity, particularly in patients with risk factors for gastrointestinal obstruction. Ondansetron is not a drug that stimulates gastric or intestinal peristalsis. It should not be used instead of nasogastric suction.

5.6 Phenylketonuria Phenylketonuric patients should be informed that ondansetron orally disintegrating tablets contain phenylalanine (a component of aspartame).

Each

4 mg orally disintegrating tablet contains 1.68 mg phenylalanine and 8 mg orally disintegrating tablet contains 3.37 mg phenylalanine.