Drug Interactions between pacritinib and paricalcitol

GENERALLY AVOID: Theoretically, coadministration with grapefruit juice may increase the plasma concentrations of pacritinib, which is primarily metabolized by CYP450 3A4. 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 the potent CYP450 3A4 inhibitor, clarithromycin. In a clinical drug interaction study, a single dose of pacritinib (400 mg) was administered following treatment with clarithromycin (500 mg twice daily for 5 days). The peak plasma concentration (Cmax) and systemic exposure (AUC) of pacritinib increased by 30% and 80%, respectively, compared to pacritinib administered alone. Longer treatment with clarithromycin that results in maximal CYP450 3A4 inhibition may increase pacritinib exposure even higher. 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 pacritinib may increase the risk of adverse effects such as diarrhea, thrombocytopenia, infection, and QT prolongation.

Pacritinib pharmacokinetics were not significantly affected when administered with a high-fat meal.

MANAGEMENT: Although clinical data are lacking, it may be advisable to avoid consumption of grapefruit or grapefruit juice during treatment with pacritinib. Pacritinib may be administered with or without food.

MONITOR: Additive effects and possible toxicity (e.g., hypercalcemia, hypercalciuria, and/or hyperphosphatemia) may occur when patients using vitamin D and/or vitamin D analogs ingest a diet high in vitamin D, calcium, and/or phosphorus. The biologically active forms of vitamin D stimulate intestinal absorption of calcium and phosphorus. This may be helpful in patients with hypocalcemia and/or hypophosphatemia. However, sudden increases in calcium or phosphorus consumption due to dietary changes could precipitate hypercalcemia and/or hyperphosphatemia. Patients with certain disease states, such as impaired renal function, may be more susceptible to toxic side effects like ectopic calcification. On the other hand, if dietary calcium is inadequate for the body's needs, the active form of vitamin D will stimulate osteoclasts to pull calcium from the bones. This may be detrimental in a patient with reduced bone density.

MANAGEMENT: Given the narrow therapeutic index of vitamin D and vitamin D analogs, the amounts of calcium, phosphorus, and vitamin D present in the patient's diet may need to be taken into consideration. Specific dietary guidance should be discussed with the patient and regular lab work should be monitored as indicated. Calcium, phosphorus, and vitamin D levels should be kept within the desired ranges, which may differ depending on the patient's condition. Patients should also be counseled on the signs and symptoms of hypervitaminosis D, hypercalcemia, and/or hyperphosphatemia.