Onzet Drug Interactions

Tablet: There is no evidence that Ondansetron either induces or inhibits the metabolism of other medical products commonly co-administered with it. Specific studies have shown that Ondansetron does not interact with alcohol, temazepam, furosemide, alfentanil, tramadol, morphine, lignocaine, propofol and thiopental. Ondansetron is metabolised by multiple hepatic cytochrome P-450 enzymes: CYP3A4, CYP2D6 and CYP1A2. Due to the multiplicity of metabolic enzymes capable of metabolising Ondansetron, enzyme inhibition or reduced activity of one enzyme (e.g. CYP2D6 genetic deficiency) is normally compensated by other enzymes and should result in little or no significant change in overall Ondansetron clearance or dose requirement.
Caution should be exercised when Ondansetron is co-administered with drugs that prolong the QT interval and/or cause electrolyte abnormalities.
Use of Ondansetron with QT prolonging drugs may result in additional QT prolongation. Concomitant use of Ondansetron with cardiotoxic drugs (e.g. anthracyclines (such as doxorubicin, daunorubicin or trastuzumab), antibiotics (such as erythromycin), antifungals (such as ketoconazole), antiarrhythmics (such as amiodarone) and beta blockers (such as atenolol or timolol) may increase the risk of arrhythmias.
Serotonergic Drugs (e.g. SSRIs and SNRIs): There have been post-marketing reports describing patients with serotonin syndrome (including altered mental status, autonomic instability and neuromuscular abnormalities) following the concomitant use of Ondansetron and other serotonergic drugs (including SSRIs and SNRIs).
Apomorphine: Based on reports of profound hypotension and loss of consciousness when Ondansetron was administered with apomorphine hydrochloride, concomitant use with apomorphine is contraindicated.
Phenytoin, Carbamazepine and Rifampicin: In patients treated with potent inducers of CYP3A4 (i.e. phenytoin, carbamazepine, and rifampicin), the oral clearance of ondansetron was increased and Ondansetron blood concentrations were decreased.
Tramadol: Data from small studies indicate that Ondansetron may reduce the analgesic effect of tramadol.
Injection: 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. On the basis of limited available data, no dosage adjustment is recommended for patients on these drugs.
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.
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.
Tramadol: Although there are no data on pharmacokinetic drug interactions between ondansetron and tramadol, data from two small studies 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 studies, leading to an increased cumulative dose in patient controlled administration (PCA) of tramadol.
Chemotherapy: In humans, carmustine, etoposide, and cisplatin do not affect the pharmacokinetics of ondansetron.
In a crossover study in 76 pediatric patients, intravenous ondansetron did not increase blood levels of high-dose methotrexate.
Temazepam: The coadministration of ondansetron had no effect on the pharmacokinetics and pharmacodynamics of temazepam.
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.