Lanthanum carbonate hydrate may increase gastric pH. It is recommended that compounds, which are known to interact with antacids, should not be taken within 2 hours of dosing with Fosrenol (e.g. chloroquine, hydroxychloroquine and ketoconazole).
In healthy subjects, the absorption and pharmacokinetics of lanthanum were not affected by co-administration of citrate.
Serum levels of fat-soluble vitamins A, D, E and K, were not affected by Fosrenol administration in clinical studies.
Human volunteer studies have shown that co-administration of Fosrenol with digoxin, warfarin or metoprolol does not produce clinically-relevant changes in the pharmacokinetic profiles of these drugs.
In simulated gastric juice, lanthanum carbonate hydrate did not form insoluble complexes with warfarin, digoxin, furosemide, phenytoin, metoprolol or enalapril, suggesting a low potential to affect the absorption of these drugs.
However, interactions with drugs such as tetracycline and doxycycline are theoretically possible and if these compounds are to be co-administered, it is recommended that they are not to be taken within 2 hours of dosing with Fosrenol.
The bioavailability of oral ciprofloxacin was decreased by approximately 50% when taken with Fosrenol in a single dose study in healthy volunteers. It is recommended that oral floxacin formulations are taken at least 2 hours before or 4 hours after Fosrenol.
Phosphate binders (including Fosrenol) have been shown to reduce the absorption of levothyroxine. Consequently, thyroid hormone replacement therapy should not be taken within 2 hours of dosing with Fosrenol and closer monitoring of TSH levels is recommended in patients receiving both medicinal products.
Lanthanum carbonate hydrate is not a substrate for cytochrome P450 and does not significantly inhibit the activities of the major human cytochrome P450 isoenzymes, CYP1A2, CYP2D6, CYP3A4, CYP2C9 or CYP2C19 in vitro.