pms-Ondansetron Drug Interactions

Drug-Drug Interactions: Specific studies have shown that there are no pharmacokinetic interactions when ondansetron is administered with alcohol, temazepam, furosemide, tramadol or propofol.
Ondansetron is metabolised by multiple hepatic cytochrome P₄₅₀ enzymes: CYP3A4, CYP2D6 and CYP1A2. Despite the multiplicity of metabolic enzymes capable of metabolising ondansetron which can compensate for an increase or decrease in enzyme activity, it was found that patients treated with inducers of CYP3A4 (i.e. phenytoin, carbamazepine, and rifampicin) demonstrated an increase in oral clearance of ondansetron and a decrease in ondansetron blood concentrations. No effect in ondansetron clearance secondary to enzyme inhibition or reduced activity (e.g., CYP2D6 genetic deficiency) has been identified to date.
QTc-Prolonging Drugs: The concomitant use of ondansetron hydrochloride with another QTc-prolonging drug should be carefully considered to determine that the therapeutic benefit outweighs the potential risk. Drugs that have been associated with QTc interval prolongation and/or torsade de pointes include, but are not limited to, the examples in the following list. Chemical/pharmacological classes are listed if some, although not necessarily all, class members have been implicated in QTc prolongation and/or torsade de pointes: Class IA antiarrhythmics (e.g., quinidine, procainamide, disopyramide); Class III antiarrhythmics (e.g., amiodarone, sotalol, ibutilide, dronedarone); Class 1C antiarrhythmics (e.g., flecainide, propafenone); antiemetics (e.g., dolasetron, droperidol, chlorpromazine, prochlorperazine); tyrosine kinase inhibitors (e.g., vandetanib, sunitinib, nilotinib, lapatinib); antipsychotics (e.g., chlorpromazine, pimozide, haloperidol, ziprasidone); antidepressants e.g., citalopram, fluoxetine, venlafaxine, tricyclic/tetracyclic antidepressants (e.g., amitriptyline, imipramine, maprotiline); opioids (e.g., methadone); domperidone; macrolide antibiotics and analogues (e.g., erythromycin, clarithromycin, telithromycin, tacrolimus); quinolone antibiotics (e.g., moxifloxacin, levofloxacin, ciprofloxacin); antimalarials (e.g., quinine, chloroquine); azole antifungals (e.g., ketoconazole, fluconazole, voriconazole); histone deacetylase inhibitors (e.g., vorinostat); beta-₂ adrenoceptor agonists (e.g., salmeterol, formoterol).
Drugs that Cause Electrolyte Abnormalities: The use of ondansetron hydrochloride with drugs that can disrupt electrolyte levels should be avoided. Such drugs include, but not limited to, the following: loop, thiazide, and related diuretics; laxatives and enemas; amphotericin B; high dose corticosteroids.
The previous lists of potentially interacting drugs are not comprehensive. Current information sources should be consulted for newly-approved drugs that prolong the QTc interval or cause electrolyte disturbances, as well as for older drugs for which these effects have recently been established.
Tramadol: Data from small studies indicate that ondansetron may reduce the analgesic effect of tramadol.
Apomorphine: Based on reports of profound hypotension and loss of consciousness when ondansetron was administered with apomorphine hydrochloride, concomitant use with apomorphine is contraindicated (see Contraindications).
Serotonergic Drugs: As with other serotonergic agents, serotonin syndrome, a potentially life-threatening condition, may occur with 5-HT₃ receptor antagonist antiemetic treatment when given in combination with other agents that may affect the serotonergic neurotransmitter system (including triptans, SSRIs, SNRIs, lithium, sibutramine, fentanyl and its analogues, dextromethorphan, tramadol, tapentadol, meperidine, methadone, and pertazocine or St. John's Wort [Hypericum perforatum]), and with drugs which impair metabolism of serotonin (such as MAOIs, including linezolid [an antibiotic which is a reversible non-selective MAOI], and methylene blue) (see Neurologic under Precautions).