An iron infusion is a medical procedure designed to deliver iron directly into the bloodstream. This method is employed when the body’s iron stores are low and oral iron supplements are not effective or cannot be tolerated. The infusion aims to quickly increase iron levels, bypassing the digestive system.
The Specific Iron Compounds
Iron is not administered as a pure, elemental form in infusions; instead, it is delivered within complex compounds featuring an iron oxyhydroxide core surrounded by a carbohydrate shell. These structures are engineered to allow for controlled release of iron within the body. Several distinct iron compounds are commonly used, each with unique characteristics influencing administration and dosage.
Ferric carboxymaltose (FCM), often known by brand names like Ferinject or Injectafer, is a non-dextran iron complex. This compound allows for the administration of large doses, typically up to 1000 mg of iron, in a single, relatively rapid infusion that can take as little as 15 minutes. Its structure minimizes the risk of certain allergic reactions sometimes associated with older iron formulations.
Iron sucrose, marketed as Venofer, represents an established intravenous iron preparation. It is a complex of iron hydroxide and sucrose and does not contain dextran. Iron sucrose is typically administered in smaller, multiple doses over several visits, commonly 200 mg per dose, often for patients with chronic kidney disease.
Iron dextran, found in products like Dexferrum and INFeD, is an older iron compound consisting of ferric hydroxide complexed with dextran. Historically, some high-molecular-weight forms carried a higher risk of severe allergic reactions, sometimes requiring a test dose. Modern low-molecular-weight iron dextran forms are still used and can deliver substantial iron doses.
Ferumoxytol, known as Feraheme, is a superparamagnetic iron oxide nanoparticle coated with a carbohydrate shell. This compound allows for rapid intravenous administration, often given as two 510 mg doses separated by a few days. Each iron compound’s design influences its stability, iron release rate, and suitability for different patient needs.
Additional Infusion Ingredients
Beyond the active iron compounds, iron infusions contain other ingredients that facilitate safe and effective delivery into the bloodstream. The most common additional component is a sterile solution, typically 0.9% sodium chloride, also known as normal saline. This saline acts as a carrier or diluent, ensuring the iron compound is properly dispersed and can be safely infused into a vein.
Some iron preparations may include inactive ingredients like pH adjusters, such as sodium hydroxide or hydrochloric acid, to maintain the solution’s acidity or alkalinity. Stabilizers, such as mannitol, can also be present to maintain the integrity and stability of the iron complex. These components are necessary for the solution’s formulation and stability, but they do not contribute directly to the iron’s therapeutic effect.
How Infused Iron Works in the Body
Once an iron compound is infused into the bloodstream, it undergoes a process within the body. The complex iron-carbohydrate structures are primarily taken up by the reticuloendothelial system. This system includes specialized cells, particularly macrophages, located in organs such as the liver, spleen, and bone marrow.
Within these cells, iron is gradually released from its carbohydrate shell. This released iron then binds to transferrin, a protein responsible for transporting iron throughout the body. Transferrin delivers iron to tissues where it is needed, especially to the bone marrow for red blood cell production. There, iron is incorporated into hemoglobin, the protein in red blood cells that carries oxygen. Any excess iron not immediately used for hemoglobin synthesis is stored as ferritin in the liver, spleen, and bone marrow, replenishing the body’s iron reserves and supporting healthy red blood cell production.