Relationship Between Iron Indices and Iron Responsiveness Following IV Ferumoxytol or Oral Iron In Patients with CKD Not on Dialysis

Iron deficiency anemia (IDA) is associated with reduced physical functioning, cardiovascular disease, and poor quality of life. The measurement of body iron stores is essential to the management of IDA, and the indices most commonly used to assess iron status are transferrin saturation (TSAT) and serum ferritin. Unfortunately, serum ferritin is not a reliable indicator of iron status, particularly in patients with chronic kidney disease (CKD), because it is an acute phase reactant and may be elevated in patients with iron deficiency in the presence of inflammation. Recent clinical trials have shown that patients with iron indices above a strict definition of iron deficiency (TSAT >15%, serum ferritin >100 ng/mL), do have a significant increase in hemoglobin (Hgb) when treated with iron. These results are consistent with recent changes to the National Cancer Comprehensive Network (NCCN) guidelines, which have expanded the definition of functional iron deficiency (relative iron deficiency) to include a serum ferritin <800 ng/mL; previously, the serum ferritin threshold was <300 ng/mL. Additionally, for patients who meet this expanded definition of functional iron deficiency (TSAT <20%, ferritin <800 ng/mL), it is now recommended that iron replacement therapy be considered in addition to erythropoiesis-stimulating agent (ESA) therapy.

Ferumoxytol (Feraheme®) Injection, a novel IV iron therapeutic agent, is indicated for the treatment of IDA in adult patients with CKD. Ferumoxytol is composed of an iron oxide with a unique carbohydrate coating (polyglucose sorbitol carboxymethylether), is isotonic, has a neutral pH, and evidence of lower free iron than other IV irons. Ferumoxytol is administered as two IV injections of 510 mg (17 mL) 3 to 8 days apart for a total cumulative dose of 1.02 g; each IV injection can be administered at a rate up to 1 mL/sec, allowing for administration of a 510 mg dose in less than 1 minute.

Data were combined from 2 identically designed and executed Phase III randomized, active-controlled, open-label studies conducted in 606 patients with CKD stages 1–5 not on dialysis. Patients were randomly assigned in a 3:1 ratio to receive a course of either 1.02 g IV ferumoxytol (n=453) administered as 2 doses of 510 mg each within 5±3 days or 200 mg of oral elemental iron (n=153) daily for 21 days. The main IDA inclusion criteria included a Hgb ≤11.0 g/dL, TSAT ≤30%, and serum ferritin ≤600 ng/mL. The mean baseline Hgb was approximately 10 g/dL, and ESAs were use by approximately 40% of patients. To further evaluate the relationship between baseline markers of iron stores and response to iron therapy, data from these trials were summarized by baseline TSAT and serum ferritin levels.

RESULTS

Overall, results from these two pooled trials show that ferumoxytol resulted in a statistically significant greater mean increase in Hgb relative to oral iron. When evaluated across the baseline iron indices examined, statistically significant (p<0.05) increases in Hgb at Day 35 were observed following ferumoxytol administration, even for subjects with baseline iron indices above levels traditionally used to define iron deficiency. Additionally, at each level of baseline iron indices, ferumoxytol produced a larger change in Hgb relative to oral iron.

These data suggest that patients with CKD not on dialysis with a wide range of iron indices at baseline respond to IV iron therapy with an increase in Hgb. Additionally, ferumoxytol consistently resulted in larger increases in Hgb relative to oral iron across all levels of baseline iron indices examined.

Adamson:VA Medical Center MC 111E: Honoraria, Membership on an entity's Board of Directors or advisory committees. Li:AMAG Pharmaceuticals, Inc.: Employment. Miller:AMAG Pharmaceuticals, Inc.: Employment. Kausz:AMAG Pharmaceuticals, Inc.: Employment.