Ferumoxytol

Absorption

Bioavailability studies were not conducted as ferumoxytol has been developed for IV administration only .
Iron therapy dosage is individualized according to specific goals for blood iron concentrations, iron storage parameters (e.g., ferritin, transferrin saturation), and serum hemoglobin concentrations. Iron toxicity is possible with excessive or unnecessary iron therapy. Systemic iron is stored in ferritin and hemosiderin, which are utilized for future production of hemoglobin. The absorption of iron depends on the route of administration. The tissue that first clears parenterally ingested iron from the plasma determines its bioavailability. If the reticuloendothelial system clears iron effectively, only small amounts will become available over time to the bone marrow. Transferrin accepts iron from the intestinal tract and also from sites of hemoglobin storage and destruction .

Toxicity

Hypersensitivity
The FDA has Feraheme (ferumoxytol) may cause serious hypersensitivity reactions, including anaphylaxis and/or anaphylactoid reactions. Serious hypersensitivity reactions were reported in 0.2% (3/1,726) of subjects administered Feraheme. Some other reactions potentially associated with hypersensitivity (e.g., pruritus, rash, urticaria or wheezing) were reported in 3.7% (63/1,726) of these subjects. It is necessary to monitor patients for signs and symptoms of hypersensitivity for at least 30 minutes following Feraheme injection and limit administration of the drug only to when personnel and therapies are readily available for the treatment of hypersensitivity reactions .
Ferumoxytol was not tested for carcinogenic effects. In general genotoxicity tests, ferumoxytol showed no evidence of mutagenic activity in an in vitro Ames test or clastogenic activity in either an in vitro chromosomal aberration assay or an in vivo micronucleus assay. No adverse effects on fertility were observed in animal studies. Ferumoxytol had no effect on male or female fertility or general reproductive function in rats .
Hypotension
Feraheme may cause significant hypotension. In a clinical study with Feraheme in patients with IDA, regardless of etiology, moderate hypotension was reported in 0.2% of subjects receiving Feraheme administered as intravenous infusion for at least 15 minutes .
Iron overload
Excessive therapy with parenteral iron may lead to excess storage of iron with a possibility of iatrogenic hemosiderosis. Frequently monitor the hematologic response during parenteral iron therapy. It is advised not to administer Feraheme to patients with iron overload .
A note on MRI studies
Administration of Feraheme may transiently affect the diagnostic ability of MR imaging. Anticipated MR imaging studies should be done before the administration of Feraheme. Alteration of MRI imaging studies may persist for up to 12 weeks after the last Feraheme dose .

The Uses of Ferumoxytol

Diagnostic aid, magnetic resonance imaging (MRI); treatment of iron deficiency.

Indications

This drug is indicated for the treatment of iron deficiency anemia in adult patients who have experienced intolerance to oral iron or have experienced an unsatisfactory response to oral iron or who have chronic kidney disease (CKD) .

Background

Ferumoxytol is an intravenously administered iron preparation indicated in the EU and the US for the treatment of iron deficiency anemia in adult patients with chronic kidney disease (CKD) .
It is comprised of superparamagnetic iron oxide nanoparticles which are coated by a semi-synthetic carbohydrate shell in an isotonic, neutral pH solution that may be administered at relatively high dose by rapid intravenous injection .

Pharmacokinetics

The pharmacodynamic effect of ferumoxytol on hematologic indexes such as Hgb (hemoglobin), serum ferritin, and TSAT (transferrin saturation) were studied and measured as primary and secondary endpoints in clinical efficacy studies .
Feraheme (ferumoxytol) reached the primary endpoint with statistical significance (p<0.001) in all three trials versus oral iron .
Ferumoxytol has been examined as a contrast agent for magnetic resonance imaging (MRI) studies. Because ferumoxytol is a very small superparamagnetic iron oxide (USPIO) with a polysaccharide coating, it may be administered via the intravenous bolus route without mast cell degranulation, which is an attributable property for magnetic resonance angiography and perfusion imaging. Unlike gadolinium, ferumoxytol crosses the blood-brain barrier at a slow pace and is considered a 'blood pool' agent. Ferumoxytol stays in the intravascular space and offers a longer time period for data acquisition during an MRI study so that data can be repeatedly obtained over a period of several minutes to hours with only small losses of intravascular signal intensity and minimal soft tissue enhancement .
Iron-containing proteins and enzymes are important in oxidation-reduction reactions, particularly those in the mitochondria. Iron is a part of myoglobin and several heme-enzymes, including the cytochromes, catalase, and peroxidase. Iron is an essential component of the metalloflavoprotein enzymes and the mitochondrial enzyme alpha-glycerophosphate oxidase. In addition, iron is a cofactor for enzymes such as aconitase and tryptophan pyrrolase. Iron deficiency cause anemia and decreased oxygen delivery. This also reduces the metabolism of muscle and decreases mitochondrial activity. Iron deficiency may also cause defects in both learning or thermoregulation. Therefore, iron is important to several metabolic functions in addition to erythropoiesis .

Metabolism

Ferumoxytol metabolism is not dependent on renal function. It is removed from the circulation by the reticuloendothelial system of the liver, spleen, and bone marrow .
Iron, bound to transferrin, is then transported in the plasma and distributed to the bone marrow for the synthesis of hemoglobin, to the reticuloendothelial system for storage, and to all cells for enzymes containing iron, and to placental cells if needed to meet fetal needs. Transferrin eventually becomes available for recycling. In normal adults, 90% of metabolized iron is conserved and reutilized repeatedly .