Drug Interaction Report

ADJUST DOSING INTERVAL: Theoretically, lanthanum carbonate may chelate with certain drugs in the gastrointestinal tract, resulting in reduced oral bioavailability of those drugs during coadministration. However, an in vitro study involving digoxin, enalapril, furosemide, metoprolol, phenytoin, and warfarin found no evidence that lanthanum carbonate forms insoluble complexes with these drugs in simulated gastric fluid. Studies in healthy subjects have also found no effect of lanthanum carbonate (1000 mg for 4 doses) on the absorption of a single dose of digoxin (0.5 mg), metoprolol (100 mg), or warfarin (10 mg).

MANAGEMENT: To minimize the potential for interaction, drugs that are known to interact with antacids (e.g., ACE inhibitors, beta blockers, bisphosphonates, coumarin derivatives, digitalis glycosides, fluoroquinolones, iron, phenytoin, rifampin, tetracyclines, thyroid preparations) should not be taken within 2 hours of administration of lanthanum carbonate according to the product labeling.

ADJUST DOSING INTERVAL: Concomitant use of some oral medications may reduce the bioavailability of orally administered iron, and vice versa.

Food taken in conjunction with oral iron supplements may reduce the bioavailability of the iron. However, in many patients intolerable gastrointestinal side effects occur necessitating administration with food.

MANAGEMENT: Ideally, iron products should be taken on an empty stomach (i.e., at least 1 hour before or 2 hours after meals), but if this is not possible, administer with meals and monitor the patient more closely for a subtherapeutic effect. Some studies suggest administration of iron with ascorbic acid may enhance bioavailability. In addition, administration of oral iron products and some oral medications should be separated whenever the bioavailability of either agent may be decreased. Consult the product labeling for specific separation times and monitor clinical responses as appropriate.

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.