Does Intravenous Iron Therapy Decrease Serum Phosphorous Levels?

Overview

Intravenous iron therapy is common and effective, with few side effects. Two formulations are used, venofer or iron sucrose and ferrlecit, or ferric gluconate. The association between intravenous iron use and decrease in serum phosphorus and vitamin D levels, with increased fractional excretion of phosphorus, has been observed with older iron preparations, such as saccharated ferric oxide. However, hypophosphatemia and osteomalacia have been reported with iron carboxymaltose, a newer iron formulation. There is no information in the literature about phosphorus and vitamin D levels after treatment with venofer or ferrlecit. We intend to check phosphorus and vitamin D serum levels in our patients prior to and after treatment with these iron formulations.

Intravenous iron replacement has become quite common in cases where oral iron therapy is insufficient or poorly tolerated. Various intravenous iron preparations have been used in patients on dialysis and with chronic kidney disease for many years, however, these patients have severely reduced glomerular filtration rate and are generally hyperphosphatemic. Although generally safe, certain iron preparations have been associated with severe phosphorus and calcitriol deficiency, caused by elevation in serum levels of fgf23, a phosphaturic humoral factor derived from osteocytes. Fractional excretion of phosphorus is indeed raised in these patients. In some cases phosphorus deficiency, or high fgf23 levels, are so severe that osteomalacia can result . This phenomenon has been observed with saccharated ferric oxide , a preparation commonly used in Japan, and in iron polymaltose . It has also been observed with iron carboxymaltose , a newer iron preparation, now available in Israel. These reports propose that iron causes elevated fgf23 levels, which in turn decreases phosphorus absorption and inhibits 1α-hydroxylase activity. Patients with deficient vitamin D have greater tendency to develop hypophosphatemia. This phenomenon of phosphorus deficiency has not been documented in the commonly used preparations of iron sucrose (venofer) and ferric gluconate (ferrlecit). These non-dextran iron preparations have a very low rate of allergic reactions and adverse events. They are used in various cases of iron deficiency anemia with normal renal function, such as patients with Inflammatory bowel disease , diabetics or in people who cannot tolerate oral iron therapy. Moreover, certain oral iron preparations are under investigation at present for their role as phosphorus binders. The purpose of this study is to measure phosphorus, parathyroid hormone and vitamin D levels in patients prior to and after intravenous iron therapy in patients with iron deficiency anemia with normal and reduced Glomerular Filtration Rate . We hypothesize that iron therapy with ferric gluconate and iron sucrose will induce hypophosphatemia and low levels of 1,25 hydroxide Vit D. We will try to ascertain whether the hypophosphatemia is clinically significant or merely a low laboratory value, and whether patients with vitamin 25 hydroxide -D deficiency have a greater propensity to develop it.