Drug Interaction Report

MONITOR: Concomitant use of immunosuppressive or myelosuppressive agents with denosumab may increase the risk of serious infections. Denosumab binds to and inhibits the receptor activator of nuclear factor kappa-B ligand (RANKL), which is expressed on activated T and B lymphocytes and in lymph nodes. Thus, denosumab alone may increase the risk of infections. In a clinical trial of over 7800 women with postmenopausal osteoporosis, the incidence of nonfatal serious infections was 3.3% in the placebo group and 4.0% in the denosumab group. Specifically, hospitalizations due to skin infections including erysipelas and cellulitis (<0.1% placebo vs. 0.4% denosumab) and serious infections in the abdomen (0.7% placebo vs. 0.9% denosumab), urinary tract (0.5% placebo vs. 0.7% denosumab), and ear (0.0% placebo vs. 0.1% denosumab) were reported. Endocarditis was reported in no placebo patients and 3 denosumab-treated patients. There was no difference in the incidence of opportunistic infections or infections resulting in death between the placebo and denosumab groups. The overall incidence of infections was also similar between the two groups.

MANAGEMENT: Caution is advised if denosumab must be used in combination with immuno- or myelosuppressive agents. Patients should be advised to contact their physician if they develop signs and symptoms of infection such as fever, chills, diarrhea, sore throat, muscle aches, shortness of breath, blood in phlegm, weight loss, red or inflamed skin, body sores, and pain or burning during urination. The need for continued denosumab therapy should be assessed when serious infections occur during treatment.

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GENERALLY AVOID: Grapefruit and/or grapefruit juice may increase the systemic exposure to palbociclib. The proposed mechanism is inhibition of CYP450 3A4-mediated first-pass metabolism in the gut wall by certain compounds present in grapefruit. Increased exposure to palbociclib may increase the risk of adverse effects such as infections, neutropenia, leukopenia, anemia, thrombocytopenia, anorexia, nausea, vomiting, diarrhea, stomatitis, alopecia, asthenia, peripheral neuropathy, and epistaxis.

ADJUST DOSING INTERVAL: Food may enhance the oral bioavailability of palbociclib capsules and reduce the intersubject variability of palbociclib exposure. According to the product labeling, absorption and exposure of palbociclib from its oral capsule formulation were very low in approximately 13% of the population when taken in the fasted state. Food intake increased the palbociclib exposure in this small subset of the population but did not alter exposure in the rest of the population to a clinically relevant extent. Compared to palbociclib capsules given under overnight fasted conditions, the population average palbociclib peak plasma concentration (Cmax) and systemic exposure (AUC) increased by 38% and 21%, respectively, when given with high-fat, high-calorie food (approximately 800 to 1000 calories; 150, 250, and 500 to 600 calories from protein, carbohydrate and fat, respectively); by 27% and 12%, respectively, when given with low-fat, low-calorie food (approximately 400 to 500 calories; 120, 250, and 28 to 35 calories from protein, carbohydrate and fat, respectively); and by 24% and 13%, respectively, when given with moderate-fat, standard calorie food (approximately 500 to 700 calories; 75 to 105, 250 to 350 and 175 to 245 calories from protein, carbohydrate and fat, respectively) one hour before and two hours after palbociclib capsule dosing.

MANAGEMENT: Patients should avoid consumption of grapefruit or grapefruit juice while on treatment with palbociclib. To avoid variability in drug absorption between doses, palbociclib capsules should be taken with food. Palbociclib tablet formulations may be taken with or without food.

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