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Overall, the safety profile of FOSRENOL has been studied in over 5200 subjects in completed clinical trials. The most common adverse reactions for FOSRENOL were gastrointestinal events, such as nausea, vomiting, and abdominal pain and they generally abated over time with continued dosing.

Clinical Trials Experience

Because clinical trials are conducted under widely varying conditions, adverse reaction rates observed in clinical trials of a drug cannot be directly compared to rates in the clinical trials of another drug and may not reflect the rates observed in practice.

In double-blind, placebo-controlled studies where a total of 180 and 95 ESRD patients were randomized to FOSRENOL and placebo, respectively, for 4-6 weeks of treatment, the most common reactions that were more frequent ( ≥ 5% difference) in the FOSRENOL group were nausea, vomiting, and abdominal pain (Table 1).

Table 1: Adverse Reactions* That Were More Common on FOSRENOL in Placebo-Controlled, Double-Blind Studies With Treatment Periods of 4-6 Weeks

Nausea 11 5
Vomiting 9 4
Abdominal pain 5 0
* expressed as the event rate for each term

In an open-label long-term 2 year extension study in 93 patients who had transitioned from other studies, resulting in a total of up to 6 years treatment, mean baseline values and changes in transaminases were similar to those observed in the earlier comparative studies, with little change during treatment.

The safety of FOSRENOL was studied in two long-term, open-labeled clinical trials, which included 1215 patients treated with FOSRENOL and 944 with alternative therapy. Fourteen percent (14%) of FOSRENOL treated patients discontinued treatment due to adverse events. Gastrointestinal adverse reactions, such as nausea, diarrhea and vomiting were the most common types of event leading to discontinuation.

In pooled active comparator controlled clinical trials, hypocalcemia was noted with an incidence of approximately 5% in both lanthanum and active comparator groups. A nonclinical study and a phase 1 study have shown reduced absorption of calcium in the intestine with lanthanum carbonate treatment.

Postmarketing Experience

The following adverse reactions have been identified during post-approval use of FOSRENOL: constipation, dyspepsia, allergic skin reactions, hypophosphatemia, and tooth injury.

Read the Fosrenol (lanthanum carbonate chewable tablets) Side Effects Center for a complete guide to possible side effects


Lanthanum in FOSRENOL has the potential to bind to drugs with anionic (e.g., carboxyl, carbonyl and hydroxyl) groups. FOSRENOL may decrease the bioavailability of tetracyclines or fluoroquinolones via this mechanism.

There are no empirical data on avoiding drug interactions between FOSRENOL and most concomitant drugs. When administering an oral medication where a reduction in the bioavailability of that medication would have a clinically significant effect on its safety or efficacy, administer the drug at least one hour before or three hours after FOSRENOL. Monitor blood levels of the concomitant drugs that have a narrow therapeutic range.

Drugs Binding to Antacids

There is a potential for FOSRENOL to interact with compounds which bind to cationic antacids (i.e. aluminum-, magnesium-, or calcium-based). Therefore, do not administer such compounds within 2 hours of dosing with FOSRENOL. Examples of relevant classes of compounds where antacids have been demonstrated to reduce bioavailability include antibiotics (such as quinolones, ampicillin and tetracyclines), thyroid hormones, ACEinhibitors, statin lipid regulators and anti-malarials.

Quinolone Antibiotics

Co-administration of FOSRENOL with quinolone antibiotics may reduce the extent of their absorption. The bioavailability of oral ciprofloxacin was decreased by approximately 50% when taken with FOSRENOL in a single dose study in healthy volunteers. Administer oral quinolone antibiotics at least 1 hour before or 4 hours after FOSRENOL. When oral quinolones are given for short courses, consider eliminating the doses of FOSRENOL that would be normally scheduled near the time of quinolone intake to improve quinolone absorption [see Pharmacokinetics].


The bioavailability of levothyroxine was decreased by approximately 40% when taken together with FOSRENOL. Administer thyroid hormone replacement therapy at least 2 hours before or 2 hours after dosing with FOSRENOL and monitor thyroid stimulating hormone (TSH) levels [see Pharmacokinetics].

Read the Fosrenol Drug Interactions Center for a complete guide to possible interactions

Last reviewed on RxList: 11/14/2012
This monograph has been modified to include the generic and brand name in many instances.


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