What is the best oral iron supplement for treating iron‑deficiency anemia?

Best Oral Iron Supplement for Iron‑Deficiency Anemia

Ferrous sulfate 200 mg once daily (providing 65 mg elemental iron) taken on an empty stomach in the morning is the gold‑standard first‑line oral iron supplement for treating iron‑deficiency anemia. 1, 2, 3

First‑Line Treatment: Ferrous Sulfate

• Ferrous sulfate remains the most cost‑effective and evidence‑based oral iron formulation, costing approximately £1.00 for a 28‑day supply compared to £47.60 for alternative preparations like ferric maltol. 1

• Each 200 mg ferrous sulfate tablet delivers 65 mg of elemental iron (324 mg total salt content), which is the standard therapeutic dose. 3

• No oral iron formulation—whether ferrous sulfate, ferrous fumarate, or ferrous gluconate—has demonstrated superiority in efficacy or tolerability; all are considered therapeutically equivalent. 1, 2

Optimal Dosing Strategy

• Take 50–100 mg elemental iron once daily in the morning on an empty stomach to maximize absorption and minimize side effects. 1, 2

• Once‑daily dosing is superior to multiple daily doses because doses ≥60 mg trigger hepcidin elevation lasting 24 hours, which blocks absorption of subsequent doses by 35–45%. 1

• Alternate‑day dosing (every other day) with 100–200 mg elemental iron markedly increases fractional iron absorption compared to daily dosing and reduces gastrointestinal side effects while maintaining efficacy. 1, 2

Alternative Ferrous Salts (If Ferrous Sulfate Not Tolerated)

• Ferrous fumarate provides 69–106 mg elemental iron per tablet and can be substituted, though evidence does not support improved tolerability over ferrous sulfate. 1, 2

• Ferrous gluconate delivers 37–38 mg elemental iron per 324 mg tablet and requires 3–4 tablets daily to achieve therapeutic dosing. 4, 2

• Switching between different ferrous salts (sulfate, fumarate, gluconate) is not supported by evidence for improving tolerability. 1

Strategies to Enhance Absorption

• Taking iron with 250–500 mg vitamin C (ascorbic acid) enhances absorption by forming a chelate with iron and preventing formation of insoluble iron compounds. 1, 2

• Avoid consuming tea or coffee within one hour of iron supplementation, as these are powerful inhibitors of iron absorption. 1, 2

• If standard doses cause intolerable gastrointestinal symptoms, taking iron with food reduces side effects but also decreases absorption. 1, 2

Formulations to Avoid

• Modified‑release iron preparations should not be prescribed because they release iron beyond the duodenum (the primary absorption site) and are classified as "less suitable for prescribing" by the British National Formulary. 1

• Multivitamin products containing ≤14 mg elemental iron are insufficient for treating iron‑deficiency anemia and should not be relied upon as the sole iron source. 1, 2

Alternative Oral Formulation: Ferric Maltol

• Ferric maltol 30 mg twice daily (total 60 mg elemental iron) can be considered for patients with documented intolerance to traditional ferrous salts, particularly those with inactive inflammatory bowel disease. 1, 2

• Ferric maltol demonstrates comparable gastrointestinal adverse events to placebo and achieves hemoglobin normalization in 63–66% of patients after 12 weeks. 1

• However, ferric maltol is substantially more expensive (£47.60 vs £1.00 per 28 days) and provides slower iron loading due to lower elemental iron content. 1

Monitoring Treatment Response

• Re‑check hemoglobin at 2 weeks after starting therapy; an increase of ≥10 g/L predicts treatment success with 90% sensitivity and 79% specificity. 1, 2

• Expect hemoglobin to rise by approximately 1 g/dL within 2 weeks in patients responding appropriately to therapy. 1, 2

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

Common Pitfalls to Avoid

• Do not prescribe multiple daily doses of iron, which significantly increase gastrointestinal symptoms (nausea, constipation, abdominal discomfort) without improving hemoglobin response. 1

• Do not continue oral iron indefinitely without monitoring; failure to achieve the expected hemoglobin rise at 2 weeks warrants investigation for non‑compliance, continued blood loss, malabsorption, or concurrent vitamin B12/folate deficiency. 1

When to Escalate to Intravenous Iron

• Intravenous iron should be considered when oral iron is contraindicated, ineffective, or not tolerated despite dose adjustments or formulation changes. 1, 2

• Intravenous iron produces a clinically meaningful hemoglobin response within one week and can replenish total body iron stores in one or two infusions with modern preparations like ferric carboxymaltose or ferric derisomaltose. 1

• Specific indications for intravenous iron include active inflammatory bowel disease, post‑bariatric surgery malabsorption, celiac disease with persistent deficiency despite gluten‑free diet, and chronic kidney disease with GFR <45 mL/min. 1, 2

Special Population: Inflammatory Bowel Disease

• Limit total elemental iron to ≤100 mg per day in patients with inflammatory bowel disease to minimize gastrointestinal irritation and avoid exacerbating disease activity. 1, 2

• Oral iron should only be prescribed when disease activity is clinically inactive; administering oral iron during active intestinal inflammation can worsen disease activity. 1

• Use transferrin saturation >50% and serum ferritin >800 µg/L as upper thresholds to guide therapy and prevent iron overload. 1