Drug Interaction Report

ADJUST DOSE: Coadministration with potent inhibitors of CYP450 3A4 may significantly increase the plasma concentrations of mifepristone, which is primarily metabolized by the isoenzyme. The clinical impact of this interaction has not been studied.

MANAGEMENT: Due to its potent antiglucocorticoid effects and potential to cause dose-related prolongation of the QT interval, extreme caution is advised when mifepristone is prescribed in combination with strong CYP450 3A4 inhibitors such as, but not limited to, itraconazole, ketoconazole, posaconazole, voriconazole, clarithromycin, conivaptan, delavirdine, nefazodone, telithromycin, and protease inhibitors. When used daily to control hyperglycemia secondary to hypercortisolism in patients with endogenous Cushing's syndrome, the dosage of mifepristone should be limited to 300 mg/day and used only when necessary.

GENERALLY AVOID: Alcohol may potentiate some of the pharmacologic effects of CNS-active agents. Use in combination may result in additive central nervous system depression and/or impairment of judgment, thinking, and psychomotor skills.

MANAGEMENT: Patients receiving CNS-active agents should be warned of this interaction and advised to avoid or limit consumption of alcohol. Ambulatory patients should be counseled to avoid hazardous activities requiring complete mental alertness and motor coordination until they know how these agents affect them, and to notify their physician if they experience excessive or prolonged CNS effects that interfere with their normal activities.

ADJUST DOSING INTERVAL: Food may significantly increase the plasma concentrations of mifepristone.

GENERALLY AVOID: Grapefruit juice may increase the plasma concentrations of mifepristone. The proposed mechanism is inhibition of CYP450 3A4-mediated first-pass metabolism in the gut wall by certain compounds present in grapefruit. Because pharmacokinetic interactions involving grapefruit juice are often subject to a high degree of interpatient variability, the extent to which a given patient may be affected is difficult to predict.

MANAGEMENT: When mifepristone is used daily to control hyperglycemia secondary to hypercortisolism in patients with endogenous Cushing's syndrome, it should be taken with food to achieve consistent plasma drug levels. Patients should be advised to avoid consuming grapefruit or grapefruit juice during treatment with mifepristone, as it may cause increased adverse effects such as headache, dizziness, fatigue, nausea, vomiting, cramping, diarrhea, hypokalemia, adrenal insufficiency, vaginal bleeding, arthralgia, peripheral edema, and hypertension. Because mifepristone is eliminated slowly from the body, the interaction with grapefruit juice may be observed for a prolonged period.