Drug Interactions between Caprelsa and droperidol / fentanyl

MONITOR CLOSELY: The use of droperidol has been associated with QT interval prolongation, torsade de pointes and other serious arrhythmias, and sudden death. The concurrent administration of agents that can produce bradycardia, a known risk factor for QT interval prolongation, such as benzodiazepines and opiates, particularly intravenous opiates, may increase the risk of QT interval prolongation. In addition, hypotensive effects and central nervous system- and/or respiratory-depressant effects may be additively or synergistically increased in patients taking droperidol with benzodiazepines or opiates, especially in elderly or debilitated patients.

MANAGEMENT: Extreme caution and close monitoring are recommended if droperidol must be administered concomitantly with other bradycardic drugs. The dosage of droperidol should be individualized and titrated to the desired effect. Routine vital sign and ECG monitoring is recommended. When droperidol is used in combination with benzodiazepines or opiates, patients should be monitored for potentially excessive or prolonged CNS or respiratory depression as well as severe hypotension. Ambulatory patients should be counseled to avoid hazardous activities requiring mental alertness and motor coordination until they know how these agents affect them, and to notify their doctor if they experience excessive or prolonged CNS effects that interfere with their normal activities.

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GENERALLY AVOID: Vandetanib can cause concentration-dependent prolongation of the QT interval. Theoretically, coadministration with other agents that can prolong the QT interval may result in additive effects and increased risk of ventricular arrhythmias including torsade de pointes and sudden death. In a phase 3 clinical trial where 231 medullary thyroid cancer patients were randomized to receive vandetanib 300 mg once daily, mean change in QTcF (Fridericia-corrected QT interval) from baseline based on the exposure-response relationship was 35 ms for the 300 mg dose. The QTcF increase remained above 30 ms for the duration of the trial (up to 2 years). In addition, 36% of patients experienced greater than 60 ms QTcF increases from baseline and 4.3% had QTcF greater than 500 ms. Vandetanib treatment alone has been associated with reported cases of torsade de pointes, ventricular tachycardia, and sudden death. In general, the risk of an individual agent or a combination of agents causing ventricular arrhythmia in association with QT prolongation is largely unpredictable but may be increased by certain underlying risk factors such as congenital long QT syndrome, cardiac disease, and electrolyte disturbances (e.g., hypokalemia, hypomagnesemia, hypocalcemia). Moreover, the extent of drug-induced QT prolongation is dependent on the particular drug(s) involved and dosage(s) of the drug(s).

MANAGEMENT: Coadministration of vandetanib with other drugs that can prolong the QT interval should generally be avoided. Should treatment with other QT-prolonging drugs be required, the manufacturer recommends more frequent monitoring of the ECG as well as serum potassium, magnesium, and calcium levels. Given vandetanib's half-life of 19 days, ECGs and serum electrolytes should typically be obtained at baseline, at 2 to 4 weeks and 8 to 12 weeks after starting treatment, and every 3 months thereafter. Vandetanib should not be started if baseline QTcF is greater than 450 ms, and treatment should be interrupted if QTcF is greater than 500 ms. Treatment may resume when QTcF returns to less than 450 ms, but at a reduced dosage. In addition, hypokalemia, hypomagnesemia, and/or hypocalcemia must be corrected prior to vandetanib administration. Since diarrhea is a common side effect of vandetanib and may cause electrolyte imbalances, ECG and electrolyte levels should also be monitored more frequently when diarrhea develops. Vandetanib treatment should be stopped in the presence of severe diarrhea. Treatment may resume when diarrhea improves, but at a reduced dosage. Following any dosage reduction, or any interruption of treatment greater than 2 weeks, QT assessment and serum electrolytes should be conducted as described previously. Patients should be advised to seek prompt medical attention if they experience symptoms that could indicate the occurrence of torsade de pointes such as dizziness, lightheadedness, fainting, palpitation, irregular heart rhythm, shortness of breath, or syncope. Because of the drug's long half-life, adverse reactions including a prolonged QT interval may not resolve quickly, thus appropriate monitoring is necessary.

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