Drug Interactions between budesonide / formoterol and letrozole / ribociclib

GENERALLY AVOID: Ribociclib can cause dose-related 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 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). 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 ribociclib with other drugs that can prolong the QT interval should generally be avoided. However, if concomitant use is required, caution and clinical and laboratory monitoring are recommended. ECGs should be assessed prior to initiation of treatment, during treatment when clinically necessary, and more frequently if QTcF prolongation occurs at any time during treatment. Ribociclib should be permanently discontinued if the QTcF interval prolongation is either greater than 500 msec or there is a greater than 60 msec change from baseline and associated with any of the following: Torsades de Pointes, polymorphic ventricular tachycardia, unexplained syncope, or signs/symptoms of serious arrhythmia. 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.

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MONITOR: Coadministration with ribociclib may increase the plasma concentrations and pharmacologic effects of drugs that are substrates of CYP450 3A4. The proposed mechanism is decreased clearance due to ribociclib-mediated inhibition of CYP450 3A4 metabolism. In healthy study subjects, administration of midazolam, a sensitive CYP450 3A4 substrate, with multiple 400 mg daily doses of ribociclib increased the midazolam peak plasma concentration (Cmax) and systemic exposure (AUC) by 2.1-fold and 3.8-fold, respectively, compared to midazolam administered alone. When given at a clinically relevant dose of 600 mg daily, ribociclib is predicted to increase midazolam Cmax and AUC by 2.4-fold and 5.2-fold, respectively.

MANAGEMENT: Caution is advised when ribociclib is used concomitantly with drugs that undergo metabolism by CYP450 3A4, particularly those with a narrow therapeutic range. Dosage adjustments as well as clinical and laboratory monitoring may be appropriate for some drugs whenever ribociclib is added to or withdrawn from therapy.

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MONITOR: Coadministration with inhibitors of CYP450 3A4 may increase the systemic bioavailability of budesonide, which undergoes extensive first-pass and systemic metabolism via intestinal and hepatic CYP450 3A4. In pharmacokinetic studies, 6- to 8-fold increases in budesonide systemic exposure (AUC) have been observed during coadministration of the potent CYP450 3A4 inhibitor ketoconazole with different oral formulations of budesonide. When ketoconazole was administered 12 hours after budesonide in one study, the AUC increase was approximately half that reported during simultaneous administration. In a prospective study of a cystic fibrosis center patient population, 11 of 25 patients receiving high-dose itraconazole (400 to 600 mg/day) and budesonide oral inhalation therapy (800 to 1600 mcg/day) were found to have adrenal insufficiency, including one who developed Cushing's syndrome, compared to none in a group of 12 patients treated with itraconazole alone. There was also no adrenal insufficiency in a group of 30 cystic fibrosis patients retrospectively included as controls, 24 of whom had been treated with high-dose inhaled budesonide for several years. Adrenal function improved, but did not normalize, in 10 of the 11 patients during a follow-up of two to ten months after discontinuation of itraconazole and institution of hydrocortisone replacement therapy. Limited pharmacokinetic data indicate that itraconazole (200 mg once daily) may increase the plasma levels of budesonide by about 4-fold following inhalation of a single 1000 mcg dose, which may be mainly due to increased bioavailability of the swallowed portion of the dose.

MANAGEMENT: The possibility of increased systemic adverse effects of budesonide should be considered during coadministration with CYP450 3A4 inhibitors. If concomitant use cannot be avoided, the dosing times between budesonide and the CYP450 3A4 inhibitor should be separated by as much as possible. In addition, the lowest effective dosage of budesonide should be prescribed, and further adjustments made as necessary according to therapeutic response and tolerance. Patients should be monitored for signs and symptoms of hypercorticism such as acne, striae, thinning of the skin, easy bruising, moon facies, dorsocervical "buffalo" hump, truncal obesity, increased appetite, acute weight gain, edema, hypertension, hirsutism, hyperhidrosis, proximal muscle wasting and weakness, glucose intolerance, exacerbation of preexisting diabetes, depression, and menstrual disorders. Other systemic glucocorticoid effects may include adrenal suppression, immunosuppression, posterior subcapsular cataracts, glaucoma, bone loss, and growth retardation in children and adolescents.

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Although they are often combined in clinical practice, the concomitant use of beta-2 adrenergic agonists and corticosteroids may result in additive hypokalemic effects. Since beta-2 agonists can sometimes cause QT interval prolongation, the development of hypokalemia may potentiate the risk of ventricular arrhythmias including torsade de pointes. However, clinical data are limited, and the potential significance is unknown. Patients who are receiving systemic or nebulized formulations of beta-2 agonists, high dosages of inhaled beta-2 agonists, or systemic corticosteroid therapy may be at a greater risk of developing hypokalemia.

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