Drug Interactions between lopinavir / ritonavir and quizartinib

ADJUST DOSE: Coadministration with potent inhibitors of CYP450 3A4 may increase the plasma concentrations of quizartinib. According to the prescribing information, quizartinib is primarily metabolized via oxidation by CYP450 3A4/5 in vitro, and its major circulating active metabolite AC886 is formed and metabolized by CYP450 3A4/5. Following coadministration of a single 53 mg dose of quizartinib with ketoconazole, a potent CYP450 3A4 inhibitor, quizartinib peak plasma concentration (Cmax) and systemic exposure (AUC) increased by 17% and 94%, respectively, while the Cmax and AUC of AC886 decreased by 60% and 94%, respectively. Increased exposure to quizartinib may increase the risk of QT interval prolongation, which has been associated with ventricular arrhythmias including torsade de pointes and sudden death.

MANAGEMENT: When concomitant use with a potent CYP450 3A4 inhibitor is required, the prescribing information recommends reducing the dosage of quizartinib. Patients prescribed 53 mg once daily should have the dosage reduced to 26.5 mg once daily, and patients prescribed 35.4 mg or 26.5 mg once daily should have the dosage reduced to 17.7 mg once daily. For patients whose current dosage is 17.7 mg once daily, treatment with quizartinib should be interrupted while the potent CYP450 3A4 inhibitor is in use and until discontinuation of the inhibitor for 5 half-lives. More frequent monitoring with electrocardiograms (ECGs) is also recommended to guide continued treatment. All patients treated with quizartinib should have ECGs performed as well as potassium and magnesium serum levels measured prior to initiation of treatment, at regular intervals during treatment, and when clinically indicated such as following dose escalation or during episodes of diarrhea or vomiting. Do not initiate quizartinib or escalate the dose if QTcF interval is greater than 450 ms. In addition, hypokalemia and hypomagnesemia should be corrected before and during treatment. If QTcF increases to greater than 480 ms during treatment, reduce the dose, interrupt therapy, or permanently discontinue quizartinib as clinically appropriate in accordance with the prescribing information. 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.

GENERALLY AVOID: Quizartinib can cause dose- and concentration-dependent prolongation of the QT interval. Theoretically, coadministration with other agents that can prolong the QT interval may increase the risk of ventricular arrhythmias including torsade de pointes and sudden death. In a clinical study where 265 patients with newly diagnosed FLT3-ITD-positive acute myeloid leukemia (AML) were treated with quizartinib (38% for >=6 months; 30% for >1 year) in combination with chemotherapy, 2.3% had a Fridericia-corrected QT interval (QTcF) greater than 500 ms and 10% had a QTcF increase from baseline greater than 60 ms. Overall, QT prolongation of any grade occurred in 14% of the quizartinib patients (compared to 4.1% of patients treated with placebo and chemotherapy), and 4% required dose reductions of quizartinib due to QT prolongation. The study excluded patients with a QTcF >=450 ms or other risk factors for QT prolongation or arrhythmic events. Based on an analysis of the exposure-response relationship, quizartinib is predicted to produce a median increase of 18 and 24 ms in the QTcF at steady-state peak plasma concentration during maintenance therapy at the 26.5 mg and 53 mg dose levels, respectively. Across premarketing clinical trials, torsade de pointes arrhythmia was reported in approximately 0.2%, cardiac arrest in 0.6% (including 0.4% with a fatal outcome), and ventricular fibrillation in 0.1% of the total 1,081 patients with AML treated with quizartinib. These severe cardiac events occurred predominantly during the induction phase. 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, hypomagnesemias). In addition, 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 quizartinib with other drugs that can prolong the QT interval should generally be avoided. If concomitant use is required, more frequent monitoring with electrocardiograms (ECGs) is recommended to guide continued treatment. All patients treated with quizartinib should have ECGs performed as well as potassium and magnesium serum levels measured prior to initiation of treatment, at regular intervals during treatment, and when clinically indicated such as following dose escalation or during episodes of diarrhea or vomiting. Do not initiate quizartinib or escalate the dose if QTcF interval is greater than 450 ms. In addition, hypokalemia and hypomagnesemia should be corrected before and during treatment. If QTcF increases to greater than 480 ms during treatment, reduce the dose, interrupt therapy, or permanently discontinue quizartinib as clinically appropriate in accordance with the prescribing information. 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. Quizartinib should be permanently discontinued in patients who experience torsade de pointes, polymorphic ventricular tachycardia, or QT prolongation with signs or symptoms of life-threatening arrhythmia.