Drug Interactions between butorphanol and Emend for Injection

MONITOR CLOSELY: Coadministration with inhibitors of CYP450 3A4 may increase the plasma concentrations of butorphanol according to the product labeling. However, pharmacokinetic data are not available. Increased butorphanol concentrations could increase or prolong adverse drug effects and may cause potentially fatal respiratory depression. Conversely, discontinuation of a CYP450 3A4 inhibitor could decrease butorphanol plasma concentrations, decrease opioid efficacy, and possibly even lead to a withdrawal syndrome in patients who had developed physical dependence to butorphanol.

MANAGEMENT: Patients receiving butorphanol with potent or moderate CYP450 3A4 inhibitors should be carefully monitored, and dosage adjustments made accordingly as needed. This is particularly important when an inhibitor is added after a stable dose of butorphanol has been achieved. Patients and/or their caregivers should be advised to seek medical attention if potential signs and symptoms of toxicity occur, such as dizziness, confusion, fainting, extreme sedation, unresponsiveness, bradycardia, slow or difficult breathing, and shortness of breath. When discontinuing CYP450 3A4 inhibitors, monitor patients closely at frequent intervals and consider increasing the opioid dosage if needed to maintain adequate analgesia or if symptoms of opioid withdrawal occur.