Iron Replacement by intravenous infusion allows for rapid delivery of all of the iron required to regenerate haemoglobin and red cell numbers, as well as provide additional iron as stores to use over months or even years. Infusion generally lasts 3-5 hours. Unlike oral iron replacement, intravenous infusion does not carry gastrointestinal side effects. It does, however, cary a risk of allergic reactions and anaphylaxis. A common side effect is a flu-like illness occurring 2-3 days after treatment. Your doctor should discuss other rare but potentially serious side effects and potential drug interactions with you prior to treatment.