Drug Interactions between atorvastatin / ezetimibe and cytarabine liposomal / daunorubicin liposomal

MONITOR: Coadministration with inhibitors of P-glycoprotein (P-gp) may increase the plasma concentrations of daunorubicin and idarubicin, both of which are substrates of the efflux transporter also known as ABCB1 or MDR1. The interaction has been studied with cyclosporine, a potent P-gp inhibitor, in attempt to overcome multidrug resistance in MDR1-overexpressing tumors. In a randomized study to test whether cyclosporine can enhance the antileukemia effect of anthracyclines, cyclosporine was found to significantly reduce the frequency of resistance to induction chemotherapy consisting of sequential cytarabine and daunorubicin (31% vs. 47%). The addition of cyclosporine also increased relapse-free and overall survival, particularly in patients with moderate or high P-gp expression. Pharmacokinetically, steady-state mean serum concentrations of daunorubicin and its active metabolite, daunorubicinol, were significantly higher (approximately 2-fold and 4-fold, respectively) in patients receiving cyclosporine. Although there was no significant difference in the frequency or severity of stomatitis or renal toxicity (as measured by creatinine elevation), grade 4 hyperbilirubinemia and grade 3 nausea occurred more frequently in patients receiving cyclosporine than in controls (31% vs. 4% and 11% vs. 3%, respectively). In a pharmacokinetic study of 27 patients with acute myelogenous leukemia receiving induction chemotherapy with idarubicin and cytarabine, the systemic exposure (AUC) to idarubicin and idarubicinol was increased by 77% and 182%, respectively, in patients administered cyclosporine 10 mg/kg daily compared to controls due to a 40% reduction in total body clearance. The interaction was also reported in another study in which increases in the AUC of idarubicin and idarubicinol were associated with increased levels of toxicity.

MANAGEMENT: Caution is advised if daunorubicin or idarubicin is prescribed in combination with a P-gp inhibitor. Patients should be closely monitored for increased adverse effects including cardiotoxicity and myelosuppression.

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MONITOR: Coadministration with ezetimibe may rarely increase the risk of myopathy and serum transaminase elevations associated with HMG-CoA reductase inhibitors (i.e., statins). The mechanism of interaction is unknown. A case report describes two patients whose serum creatine kinase increased after ezetimibe was added to their statin therapy (atorvastatin and fluvastatin, respectively). One of the patients also developed myalgia and tendinopathy, which resolved promptly after withdrawal of both drugs. Statin therapy was subsequently reintroduced at the previous dosage without incident. In the other patient, serum creatine kinase returned to normal within 4 weeks after discontinuation of ezetimibe while the statin was continued. On the contrary, no cases of myopathy or tendinopathy occurred in a study of 33 hypercholesterolemic patients treated with ezetimibe and atorvastatin or simvastatin. There were also no reports of myopathy or significant increases in serum creatine kinase in a study of 32 subjects treated with ezetimibe and fluvastatin. In controlled clinical studies, the incidence of consecutive elevations (greater than 3 times the upper limit of normal) in serum transaminases was 1.3% for patients treated with ezetimibe in combination with a statin versus 0.4% for patients treated with a statin alone. These elevations were generally asymptomatic, not associated with cholestasis, and returned to baseline after discontinuation of therapy or with continued treatment.

MANAGEMENT: Until further information is available, use of a statin in combination with ezetimibe should be approached with caution. Patients should be advised to promptly report to their physician any unexplained muscle pain, tenderness, or weakness, particularly if accompanied by malaise or fever. The drugs should be discontinued if creatine kinase is markedly elevated in the absence of strenuous exercise or if myopathy is otherwise suspected or diagnosed. In addition, liver function tests should be performed at initiation of therapy and according to the recommendations of the HMG-CoA reductase inhibitor.

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MONITOR: The concomitant or sequential administration of multiple antineoplastic agents may result in additive toxicities, particularly in the bone marrow, gastrointestinal tract and heart.

MANAGEMENT: Close clinical and laboratory monitoring for hematologic and nonhematologic toxicities are recommended when antineoplastic agents are administered concurrently or during close intervals. Dosing adjustments may be necessary. The manufacturers' recommendations and institutional protocols for dosage, treatment regimens, monitoring, and management of toxicities should be consulted.

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