The FDA has approved the sodium/hydrogen exchanger 3 (NHE3) inhibitor tenapanor (Xphozah – Ardelyx) to reduce serum phosphorus in adults with chronic kidney disease (CKD) on dialysis as add-on therapy when phosphate binders are ineffective or as monotherapy when phosphate binders cannot be tolerated. Tenapanor is the first NHE3 inhibitor to be approved in the US for hyperphosphatemia. It was previously approved as Ibsrela to treat irritable bowel syndrome with constipation (IBS-C).

Primary hypothyroidism is usually the result of Hashimoto's thyroiditis, thyroidectomy, or radioactive iodine therapy. Treatment of hypothyroidism with replacement doses of thyroid hormone is usually lifelong. Levothyroxine is the drug of choice.

Sevelamer carbonate (Renvela – Genzyme), a buffered form of the anion-exchange resin sevelamer hydrochloride (Renagel – Genzyme),1 has been approved by the FDA for use in patients with chronic kidney disease on dialysis. According to the manufacturer, Renvela will replace Renagel, which has been shown to induce or exacerbate metabolic acidosis in patients on dialysis. Two randomized, crossover studies found the two sevelamer salts equivalent in their ability to lower serum phosphate.2,3 Patients taking the carbonate had higher serum bicarbonate concentrations and fewer gastrointestinal adverse effects. Sevelamer carbonate, which is available in 800-mg tablets, can be substituted for the hydrochloride salt gram for gram. Recent studies in patients beginning hemodialysis have suggested a possible mortality benefit for sevelamer compared to less expensive calcium- based phosphate binders,4,5 but some critics are skeptical.6

1. Phosphate binders. Med Lett Drugs Ther 2006; 48:15.
2. J Delmez et al. A randomized, double-blind, crossover design study of sevelamer hydrochloride and sevelamer carbonate in patients on hemodialysis. Clin Nephrol 2007; 68:386.
3. S Fan et al. Renvela (sevelamer carbonate) powder and Renagel (sevelamer hydrochloride) tablets: report of a randomized, cross-over study in chronic kidney disease (CKD) patients on hemodialysis (poster). American Society of Nephrology Renal Week. October 31- November 5 2007. San Francisco.
4. GA Block et al. Mortality effect of coronary calcification and phosphate binder choice in incident hemodialysis patients. Kidney Int 2007; 71:438.
5. AM Borzecki et al. Survival in end stage renal disease: calcium carbonate vs. sevelamer. J Clin Pharm Ther 2007; 32:617.
6. J Silver. The details bedevil DCOR. Kidney Int 2007; 72:1041.

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Hyperphosphatemia in end-stage renal disease can lead to secondary hyperparathyroidism, renal osteodystrophy, metastatic calcification and cardiovascular mortality. addition to dietary restriction of phosphorus and hemodialysis, drugs that bind phosphates in the gut are usually needed as well. Aluminum hydroxide is no longer recommended for long-term use because of concerns about its toxicity.