Cal-Os/Cal-Os Plus D/Cal-Os Chew Drug Interactions

Calcium salts interact with many other drugs both by alterations in gastric pH and emptying, and by formation of complexes that are not absorbed. Interactions can be minimized by giving Calcium carbonate and any other medication 2 to 3 hours (for Cal-Os Plus D) or 4 hours (for Cal-Os Chew) apart.
Bisphosphonates: Concomitant administration of calcium salts with bisphosphonates (e.g., alendronate, etidronate, ibandronate, risedronate) may reduce absorption of the bisphosphonate from the GI tract. To minimize this effect, the drug should be administered at separate times (for Cal-Os Plus D) or at least 2 hours after bisphosphonates administration (for Cal-Os Chew).
Cardiac Glycosides: The inotropic and toxic effect of cardiac glycosides and calcium are synergistic and arrhythmias may occur if these drugs are given together.
Iron preparations: Concomitant administration of calcium salts and oral iron preparations may result in reduced absorption of iron. Patients should be advised to take the drugs at different times, whenever possible.
Levothyroxine: Calcium carbonate may form an insoluble chelate with levothyroxine, resulting in decreased levothyroxine absorption and increased serum thyrotropin (thyroid stimulating hormone) concentrations. To minimize or prevent this interaction, oral levothyroxine sodium should be administered at least 4 hours apart from Calcium carbonate.
Quinolones: Concomitant administration of calcium salts and some fluoroquinolones (e.g., ciprofloxacin) may reduce oral bioavailability of the fluoroquinolone.
Tetracyclines: Calcium complexes tetracycline antibiotics rendering them inactive; the two drugs should not be given at the same time orally.
Cal-Os Plus D: Cholestyramine or colestipol hydrochloride: Cholestyramine or colestipol hydrochloride administration may result in decreased intestinal absorption of vitamin D analogs; patients taking cholestyramine or colestipol hydrochloride should be instructed to allow as long a time interval as possible between the ingestion of vitamin D analogs and the resin.
Orlistat: Orlistat may result in decreased GI absorption of vitamin D analogs. At least 2 hours should elapse between (before or after) any orlistat dose and vitamin D analog administration.
Mineral oil: Mineral oil may interfere with intestinal absorption of vitamin D analogs. Patients taking mineral oil should be instructed to allow as long a time interval as possible between the ingestion of vitamin D analogs and mineral oil.
Drugs that inhibit cytochrome P-450 enzymes: Drugs that inhibit CYP enzymes (e.g., atazanavir, clarithromycin, indinavir, itraconazole, ketoconazole, nefazodone, nelfinavir, ritonavir, saquinavir, telithromycin, voriconazole) may inhibit CYP27B1, which metabolizes calcifediol to its activated form (1,25-dihydroxycholecalciferol [calcitriol]), and CYP24A1, which metabolizes both calcifediol and 1,25-dihydroxycholecalciferol to inactive metabolites, thereby altering serum calcifediol concentrations.
Drugs that induce hepatic microsomal enzymes: Administration of anticonvulsants ( e.g., carbamazepine, phenobarbital, phenytoin) and other drugs that induce hepatic microsomal hydroxylation may decrease plasma concentrations of 25-hydroxylated ergocalciferol and 25- hydroxylated cholecalciferol (calcifediol) and increase metabolism of the vitamins to inactive metabolites. Dosage adjustment of vitamin D analogs may be required. Serum concentrations of total 25-hydroxyvitamin D, iPTH, and calcium should be monitored in patients receiving calcifediol when concomitant therapy with anticonvulsants or other drugs that stimulate microsomal hydroxylation is initiated or discontinued.
Thiazide diuretics: Concurrent administration of thiazide diuretics and pharmacologic doses of vitamin D analogs in patients with hypoparathyroidism may result in hypercalcemia which may be transient and self-limited or may require discontinuance of vitamin D analogs. Thiazide-induced hypercalcemia in hypoparathyroid patients is probably caused by increased release of calcium from bone. Thiazide diuretics also can induce hypercalcemia by decreasing renal calcium excretion. More frequent monitoring of serum calcium concentrations may be required in patients with secondary hyperparathyroidism and chronic kidney disease receiving such concomitant therapy.
Corticosteroids: Corticosteroids counteract the effects of vitamin D analogs.
Cardiac glycosides: Concurrent use of vitamin D analogs and cardiac glycosides may result in cardiac arrhythmias.