What is the recommended dosage of iron supplements for iron deficiency anemia?

Recommended Dosage of Iron Supplements for Iron Deficiency Anemia

For iron deficiency anemia in adults, prescribe 50-100 mg of elemental iron once daily, taken in the morning on an empty stomach, and continue for 3 months after hemoglobin normalizes to replenish iron stores. 1

Optimal Dosing Strategy

Standard Dosing

• Start with 50-100 mg elemental iron once daily (e.g., one ferrous sulfate 200 mg tablet = 65 mg elemental iron) 1
• Take in the fasting state (morning) for optimal absorption 1
• This represents a significant departure from older guidelines that recommended 200 mg three times daily 1

Rationale for Lower, Once-Daily Dosing

The British Society of Gastroenterology (2021) guidelines emphasize that oral doses ≥60 mg elemental iron stimulate hepcidin levels, reducing subsequent iron absorption by 35-45% 1. This means higher or more frequent dosing does not proportionally increase absorption and may worsen side effects 1.

Alternative Dosing for Intolerance

• If gastrointestinal side effects occur, switch to alternate-day dosing (one tablet every other day) rather than changing iron formulations 1
• Alternate-day administration of 100-200 mg elemental iron significantly increases fractional iron absorption compared to daily dosing 1
• Do not give afternoon or evening doses after a morning dose, as circadian hepcidin increases reduce absorption 2

Treatment Duration

Continue oral iron for approximately 3 months after hemoglobin normalization to ensure adequate repletion of marrow iron stores 1. The older recommendation of 2-3 months remains acceptable 1, 3.

Monitoring Protocol

• Check hemoglobin response at 4 weeks 1
• Hemoglobin should rise by approximately 2 g/dL after 3-4 weeks 1
• After normalization, monitor blood count every 3 months for 1 year, then at 6-month intervals 1

When Standard Oral Therapy Fails

If no hemoglobin response after 4 weeks despite compliance and absence of acute illness, consider 1:

• Reduced dose with alternate-day dosing
• Alternative oral preparations (ferric maltol for inflammatory bowel disease patients)
• Parenteral iron when oral iron is contraindicated, ineffective, or not tolerated

Common Formulations and Elemental Iron Content

From the British Society of Gastroenterology guidelines 1:

• Ferrous sulfate 200 mg tablet = 65 mg elemental iron
• Ferrous sulfate 325 mg MR tablet = 105 mg elemental iron 4
• Ferrous fumarate 210 mg tablet = 69 mg elemental iron
• Ferrous fumarate 322 mg tablet = 106 mg elemental iron
• Ferrous gluconate 300 mg tablet = 37 mg elemental iron 5

Special Populations

Pregnant Women

• Start 30 mg/day elemental iron at first prenatal visit for prevention 1
• For treatment of anemia: 60-120 mg/day elemental iron 1
• Reduce to 30 mg/day once hemoglobin normalizes for gestational stage 1

Adolescent Girls and Non-Pregnant Women

• 60-120 mg/day elemental iron for treatment of anemia 1
• Continue for 2-3 months after correction 1

Critical Pitfalls to Avoid

• Do not prescribe traditional high-dose regimens (200 mg three times daily) as they reduce absorption and increase side effects 1
• Do not switch between different ferrous salts for intolerance—this is not evidence-based; instead use alternate-day dosing 1
• Do not use modified-release preparations as first-line, as they may release iron beyond the duodenum where absorption is optimal 1
• Do not give iron with food initially unless side effects necessitate it, as this reduces absorption 1