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The aim of the study is to compare two accepted treatments for iron deficiency anemia (oral ferrous sulfate and intravenous ferumoxytol) for efficacy and speed of response in the treatment of iron deficiency anemia (IDA) in the post-operative bariatric surgical patient. In this study, 104 bariatric surgical post-operative patients will be randomly assigned 52 each to oral or 52 to a single dose IV iron treatment using double-blind procedures.

Rationale for study: The preponderance of published evidence reports superior efficacy and decreased toxicity of intravenous iron compared to oral iron in correcting anemia and iron parameters in published trials of bariatric surgery patients. Intravenous, and not oral, iron ensures adequate delivery and avoids gastrointestinal toxicities, which may be especially burdensome in these patients who require optimal levels of energy to maintain prudent exercise programs recommended by patients' bariatric practitioners. Uncontradicted published evidence reports safety and efficacy of complete replacement doses of intravenous iron administered in one or two doses of either low molecular weight iron dextran, ferumoxytol, ferric carboxymaltose or iron isomaltoside. A common feature of all studies extant is the lack of reported serious adverse events. Even in patients with minimally invasive procedures such as gastric banding or stapling in whom oral iron may be tolerated, given the often present multiple gastrointestinal perturbations, intravenous iron may simplify care.

Drugs used: The investigators propose to use and FDA approved IV iron preparation - ferumoxytol, administered as two doses (over a interval of 2 to 7 days), each 510 mg over fifteen minutes based on published prospective safety and efficacy data and compare the effectiveness of the treatment to the American Metabolic and Bariatric Associations recommended treatment for iron deficiency anemia in the post-operative bariatric patients of oral iron ferrous sulphate 325 mg twice daily for 6 weeks.

Inclusion Criteria:

• Aged ≥ 18 years
• Patients who have undergone a Roux-en Y Gastric Bypass or Vertical Sleeve Gastrectomy and are at least 3 months or more out from surgery.
• Iron deficiency anemia defined as iron deficient with either ferritin < 20 mcg/l, transferrin saturation (TSAT) < 19%, or anemia with Hgb < 13 g/dL for both males and females.
• Willingness to use contraceptive to avoid pregnancy: Women have to be surgically sterile, post menopausal or use one of the following contraceptives during the whole study period and after the study has ended for at least five times the plasma biological half-life of the investigational medicinal product: intrauterine devices or hormonal contraceptives (contraceptive pills, implants, transdermal patches, hormonal vaginal devices, or injections with prolonged release).
• Willingness to participate and signing the informed consent form.

Exclusion Criteria:

• Iron overload or disturbances in utilization of iron (e.g. hemochromatosis and hemosiderosis)
• Decompensated liver cirrhosis or active hepatitis (ALT > 3 times upper limit of normal)
• Serum ferritin > 500 ng/mL or transferrin saturation > 40%
• Active acute or chronic infections (assessed by clinical judgment that may be indicated by White Blood Cells (WBC) and C-Reactive Protein (CRP) when these are available)
• Rheumatoid arthritis with symptoms or signs of active inflammation
• Pregnant and nursing women
• History of multiple allergies
• Known hypersensitivity to ferumoxytol or oral iron or any excipients in the drug products
• Previous IV iron treatment for IDA
• Other iron treatment or blood transfusion within 4 weeks prior to the screening or treatment visit
• Planned elective surgery during the study
• Any other medical condition that, in the opinion of Investigator, may cause the subject to be unsuitable for the completion of the study or place the subject at potential risk from being in the study, e.g. a malignancy, uncontrolled hypertension, unstable ischemic heart disease, or uncontrolled diabetes mellitus

The IV bags will be opaque and patients will be asked to wear a eye mask during the infusion of iron vs. saline.

The oral tables will be identical in color and shape (iron in the form of ferrous sulphate and vitamin C)