Ferrous Sulfate Dosage for Iron Deficiency Anemia
Start ferrous sulfate 200 mg (65 mg elemental iron) once daily—this is the evidence-based first-line treatment for iron deficiency anemia. 1, 2, 3
Optimal Dosing Strategy
Prescribe once-daily dosing, never multiple times per day, as once-daily administration improves tolerance while maintaining equal or better iron absorption due to hepcidin regulation that blocks further absorption for 48 hours after iron intake 1, 4
Ferrous sulfate 325 mg tablets contain 65 mg of elemental iron, providing 362% of the U.S. recommended daily intake 2
Alternate-day dosing (every other day) is an acceptable alternative that increases fractional iron absorption and improves tolerance with similar efficacy if daily dosing causes side effects 1, 4
Enhancing Absorption
Add vitamin C (ascorbic acid) 500 mg with each iron dose to enhance absorption, particularly critical when transferrin saturation is low 1, 3, 4
Take iron on an empty stomach for optimal absorption, but taking with food is acceptable if gastrointestinal side effects (nausea, constipation, dyspepsia) occur 1
Expected Response and Duration
Check hemoglobin at 4 weeks—expect a rise of approximately 2 g/dL 1, 5, 4
Continue oral iron for 3 months after hemoglobin normalizes to fully replenish iron stores, not just until anemia resolves 1, 3, 4
If hemoglobin has not increased by at least 1 g/dL after 4 weeks, assess for non-adherence, ongoing blood loss, malabsorption, or inflammatory conditions blocking absorption 5
Alternative Oral Formulations
Ferrous gluconate (38 mg elemental iron per 325 mg tablet) or ferrous fumarate (106 mg elemental iron per 325 mg tablet) are equally effective alternatives if ferrous sulfate is not tolerated, though typically more expensive 1, 4
No single oral iron formulation has any therapeutic advantage over another—the choice is purely economic 1
When to Switch to Intravenous Iron
Switch to IV iron if any of the following apply:
Intolerance to at least two different oral iron preparations 1, 5, 3
No hemoglobin rise after 4 weeks of documented adherence to oral therapy 5
Active inflammatory bowel disease with hemoglobin <10 g/dL 1, 3
Post-bariatric surgery patients due to disrupted duodenal absorption 1, 3
Celiac disease with inadequate response to oral iron despite gluten-free diet adherence 1
Chronic kidney disease or heart failure with functional iron deficiency 1, 3
Ongoing gastrointestinal blood loss exceeding oral replacement capacity 1
Second and third trimesters of pregnancy if oral iron fails 3, 4
Preferred IV Iron Formulations
Choose IV iron preparations that replace iron deficits in 1-2 infusions rather than multiple infusions to minimize risk 1
Ferric carboxymaltose (500-1000 mg single doses over 15 minutes) or iron dextran as total dose infusion are preferred options 1
True anaphylaxis risk is very rare (0.6-0.7%); most reactions are infusion-related and respond to slowing the infusion rate 1
Critical Pitfalls to Avoid
Do not prescribe multiple daily doses (e.g., three times daily)—this increases side effects without improving efficacy due to hepcidin-mediated absorption blockade 1, 4
Do not stop iron therapy when hemoglobin normalizes—continue for 3 months to replenish stores 1, 5, 4
Do not continue ineffective oral iron beyond 4 weeks—reassess and switch to IV iron if no response 5
Do not overlook vitamin C supplementation when oral iron response is suboptimal 1, 4
Do not fail to identify and treat the underlying cause of iron deficiency while supplementing 1, 4