What type of oral iron supplement is recommended for treating iron deficiency anemia?

Oral Iron for Iron Deficiency Anemia

Start with ferrous sulfate 200 mg (65 mg elemental iron) once daily, taken on an empty stomach—this is the most cost-effective first-line treatment recommended by major gastroenterology societies. 1

First-Line Iron Formulation

• Ferrous sulfate is the preferred initial choice because it provides 65 mg elemental iron per 200 mg tablet and costs approximately £1.00 for a 28-day supply, making it significantly more economical than alternatives. 1, 2

• Alternative ferrous salts (ferrous fumarate providing 69-106 mg elemental iron, or ferrous gluconate providing 37 mg elemental iron) are equally effective if ferrous sulfate is not tolerated. 1, 2

• There is no evidence that any single oral iron formulation is superior to others in terms of effectiveness or tolerability—the choice should be guided primarily by cost and availability. 1, 2

Optimal Dosing Strategy

• Take one tablet daily (50-100 mg elemental iron) rather than multiple doses per day. 1 This recommendation is based on physiological evidence showing that oral iron increases serum hepcidin levels for up to 48 hours, which blocks further iron absorption. 1, 2

• Taking iron more frequently than once daily does not improve absorption but significantly increases gastrointestinal side effects. 1

• Administer on an empty stomach to maximize absorption, though this may increase GI side effects. 1

• If once-daily dosing is not tolerated, alternate-day dosing (every other day) leads to significantly increased fractional iron absorption and lower rates of nausea compared to daily dosing. 1, 2

Enhancing Absorption

• Take iron with 250-500 mg vitamin C (ascorbic acid) to enhance absorption by forming a chelate with iron and reducing ferric to ferrous iron. 1, 2

• Avoid tea and coffee within one hour of taking iron as they are powerful inhibitors of iron absorption. 1, 2

• Avoid taking iron with calcium-containing foods or medications, which significantly reduce absorption. 2

Monitoring Response

• Check hemoglobin at 4 weeks—expect an increase of at least 1 g/dL (10 g/L) within 2 weeks if the patient is responding. 1, 2

• The absence of a hemoglobin rise of at least 10 g/L after 2 weeks strongly predicts subsequent treatment failure (sensitivity 90.1%, specificity 79.3%). 1, 2

• Continue treatment for approximately 3 months after hemoglobin normalizes to ensure adequate replenishment of marrow iron stores. 1, 2

When Standard Oral Iron Fails

If the patient does not tolerate standard ferrous salts or fails to respond:

• Consider ferric maltol (30 mg twice daily) for patients with previous intolerance to traditional iron salts, particularly those with inactive inflammatory bowel disease and moderate anemia (Hb >95 g/L). 1 However, this costs £47.60 versus £1.00 for ferrous sulfate per 28 days. 1

• Avoid modified-release preparations—these are indicated as "less suitable for prescribing" in the British National Formulary. 1, 2

• Do not rely on multivitamin preparations as they typically contain insufficient elemental iron (up to 14 mg) for treating iron deficiency anemia. 1, 2

When to Switch to Intravenous Iron

Consider parenteral iron when:

• Oral iron is contraindicated, ineffective, or not tolerated despite modifications. 1, 2

• Ferritin levels do not improve after an adequate trial of oral iron. 1, 2

• The patient has conditions impairing oral iron absorption (inflammatory bowel disease, post-bariatric surgery, celiac disease, atrophic gastritis). 1, 3

• There is ongoing blood loss exceeding oral iron absorption capacity. 1

• The patient has chronic inflammatory conditions (chronic kidney disease, heart failure, inflammatory bowel disease, cancer). 1, 3

Common Pitfalls to Avoid

• Do not prescribe ferrous sulfate three times daily—the older guideline recommendation of 200 mg three times daily is outdated. 1 Current evidence supports once-daily dosing based on hepcidin physiology. 1

• Do not switch between different traditional iron salts (e.g., from ferrous sulfate to ferrous fumarate) expecting better tolerance—this practice is not supported by evidence. 1

• Do not defer iron replacement while awaiting investigations unless colonoscopy is imminent. 1

• Recognize that gastrointestinal side effects (constipation 12%, diarrhea 8%, nausea 11%) are common with all oral iron preparations. 1