Drug Interactions between alendronate / cholecalciferol and lanthanum carbonate

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.

ADJUST DOSING INTERVAL: Food significantly decreases the bioavailability of alendronate, possibly to negligible levels.

MANAGEMENT: Alendronate should be administered with 6 to 8 ounces of plain water, at least 30 minutes before the first food, beverage, or medication of the day. Patients should remain upright for at least 30 minutes following administration of alendronate.

GENERALLY AVOID: Lanthanum carbonate should be administered with food for therapeutic efficacy. However, it is insoluble in water (<0.01 mg/mL at pH 7.5) and therefore cannot be dissolved in liquid for administration through an enteral feeding tube, because it may result in blockage of the tube.

MANAGEMENT: Administration of lanthanum carbonate with enteral feedings is not recommended. Alternative medications such as calcium carbonate suspension should be considered.