Drug Interactions between abemaciclib and Tylenol

GENERALLY AVOID: Chronic, excessive consumption of alcohol may increase the risk of acetaminophen-induced hepatotoxicity, which has included rare cases of fatal hepatitis and frank hepatic failure requiring liver transplantation. The proposed mechanism is induction of hepatic microsomal enzymes during chronic alcohol use, which may result in accelerated metabolism of acetaminophen and increased production of potentially hepatotoxic metabolites.

MANAGEMENT: In general, chronic alcoholics should avoid regular or excessive use of acetaminophen. Alternative analgesic/antipyretic therapy may be appropriate in patients who consume three or more alcoholic drinks per day. However, if acetaminophen is used, these patients should be cautioned not to exceed the recommended dosage (maximum 4 g/day in adults and children 12 years of age or older).

GENERALLY AVOID: Grapefruit juice may increase the plasma concentrations of abemaciclib. The proposed mechanism is inhibition of CYP450 3A4-mediated first-pass metabolism in the gut wall by certain compounds present in grapefruit. Inhibition of hepatic CYP450 3A4 may also contribute. The interaction has not been studied with grapefruit juice, but has been reported for other CYP450 3A4 inhibitors. According to the product labeling, abemaciclib systemic exposure (AUC) is predicted to increase by up to 16-fold when administered with the potent CYP450 3A4 inhibitor ketoconazole. Itraconazole, another potent inhibitor, is predicted to increase the relative potency-adjusted unbound AUC of abemaciclib plus its active metabolites by 2.2-fold. In cancer patients, administration of a single 50 mg dose of abemaciclib (one-third the approved recommended dose of 150 mg) with clarithromycin 500 mg twice daily increased the relative potency-adjusted unbound AUC of abemaciclib plus its active metabolites by 2.5-fold relative to abemaciclib administered alone. The moderate CYP450 3A4 inhibitors, diltiazem and verapamil, are predicted to increase the relative potency-adjusted unbound AUC of abemaciclib plus its active metabolites by 2.4-fold and 1.6-fold, respectively. In general, the effect of grapefruit juice is concentration-, dose- and preparation-dependent, and can vary widely among brands. Certain preparations of grapefruit juice (e.g., high dose, double strength) have sometimes demonstrated potent inhibition of CYP450 3A4, while other preparations (e.g., low dose, single strength) have typically demonstrated moderate inhibition. Increased exposure to abemaciclib may increase adverse effects such as nausea, vomiting, diarrhea, stomatitis, venous thromboembolism, hepatotoxicity, anemia, neutropenia, and thrombocytopenia.

Food has modest effects on the pharmacokinetics of abemaciclib. A high-fat, high-calorie meal (800 to 1000 calories; 150 calories from protein, 250 calories from carbohydrate, and 500 to 600 calories from fat) administered to healthy subjects increased the Cmax and AUC of abemaciclib plus its active metabolites by 26% and 9%, respectively.

MANAGEMENT: Abemaciclib may be administered with or without food. Patients should avoid consumption of grapefruit and grapefruit juice during treatment with abemaciclib.

MONITOR: Smoking cessation may lead to elevated plasma concentrations and enhanced pharmacologic effects of drugs that are substrates of CYP450 1A2 (and possibly CYP450 1A1) and/or certain drugs with a narrow therapeutic index (e.g., flecainide, pentazocine). One proposed mechanism is related to the loss of CYP450 1A2 and 1A1 induction by polycyclic aromatic hydrocarbons in tobacco smoke; when smoking cessation agents are initiated and smoking stops, the metabolism of certain drugs may decrease leading to increased plasma concentrations. The mechanism by which smoking cessation affects narrow therapeutic index drugs that are not known substrates of CYP450 1A2 or 1A1 is unknown. The clinical significance of this interaction is unknown as clinical data are lacking.

MANAGEMENT: Until more information is available, caution is advisable if smoking cessation agents are used concomitantly with drugs that are substrates of CYP450 1A2 or 1A1 and/or those with a narrow therapeutic range. Patients receiving smoking cessation agents may require periodic dose adjustments and closer clinical and laboratory monitoring of medications that are substrates of CYP450 1A2 or 1A1.