Drug Interactions between Docefrez and zafirlukast

MONITOR: Coadministration with inhibitors of CYP450 3A4 or dual CYP450 3A4 and P-glycoprotein (P-gp) inhibitors may increase the plasma concentrations of docetaxel, which is a substrate of both CYP450 3A4 and P-gp. In a pharmacokinetic study consisting of 7 cancer patients, mean dose-normalized docetaxel systemic exposure (AUC) increased by 2.2-fold and clearance decreased by 49% when intravenous docetaxel was given at a reduced dosage of 10 g/m2 in combination with the potent CYP450 3A4 inhibitor ketoconazole (200 mg orally once daily for 3 days) compared to docetaxel administered alone at 100 mg/m2. In addition, a suspected interaction with amiodarone was described in a case report involving a 77-year-old woman with HER2-positive invasive ductal breast cancer on long-term amiodarone therapy who developed increasing abdominal discomfort and skin lesions during 4 cycles of paclitaxel (80 mg/m2 weekly) and trastuzumab. A subsequent switch to docetaxel (100 mg or 75 mg/m2 weekly) led to the development of severe skin and mucosal toxicity, requiring hospitalization 8 days after the first docetaxel dose was administered. Analysis of two blood samples taken 9 and 10 days after docetaxel administration showed an approximately fivefold increase in its AUC as well as the presence of paclitaxel in unquantifiable levels, 20 and 21 days after it was last administered. In another case report, a 79-year-old man was hospitalized with fever, diarrhea, and grade 4 stomatitis and neutropenia after receiving a third cycle of docetaxel (35 mg/m2 on days 1 and 8 every 21 days) for metastatic androgen-independent prostate cancer while on dronedarone therapy (400 mg twice daily), which had been commenced 24 days earlier due to recurrence of atrial fibrillation. Docetaxel was still detectable in a plasma sample taken 24 days after it was last administered, at a concentration of approximately 2.4 ng/mL, even though its terminal half-life is about 12 hours. Unfortunately, the patient died after deterioration of his condition and multiple infectious complications. The authors of these case reports propose that, in addition to CYP450 3A4 inhibition, P-gp inhibition due to amiodarone and dronedarone may also have contributed to the interaction.

MANAGEMENT: Caution is advised if docetaxel is prescribed in combination with CYP450 3A4 inhibitors or dual CYP450 3A4 and P-gp inhibitors. Patients should be closely monitored for the development of docetaxel toxicity such as myelosuppression, stomatitis, neurotoxicity (e.g., paresthesia, dysesthesia, pain), myalgia, asthenia, fluid retention, nausea, vomiting, and diarrhea. Dosage reduction of docetaxel may be required if an interaction is suspected.

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