What is the recommended dose of ferrous gluconate (iron supplement) for adults?

Ferrous Gluconate Dosing for Adults

For adults with iron deficiency anemia, ferrous gluconate should be dosed at 300-325 mg tablets (containing 35-38 mg elemental iron) taken once daily on an empty stomach, requiring 3-4 tablets daily to achieve the recommended 100-150 mg of elemental iron per day. 1, 2

Understanding Elemental Iron Content

• Ferrous gluconate 300-325 mg tablets contain only 35-38 mg of elemental iron per tablet, which is significantly less than other common iron preparations 1, 2
• This is substantially lower than ferrous sulfate (65 mg elemental iron per 325 mg tablet) or ferrous fumarate (106-108 mg elemental iron per 325 mg tablet) 1, 3

Recommended Dosing Strategy

To achieve adequate iron repletion, adults need 50-100 mg elemental iron once daily, which translates to approximately 3-4 tablets of ferrous gluconate (300-325 mg) taken together as a single daily dose. 1, 3, 4

• The British Society of Gastroenterology recommends 50-100 mg elemental iron once daily for moderately severe anemia 1
• The FDA label for ferrous gluconate specifies 1 tablet three to four times daily, but modern evidence supports once-daily dosing for better absorption and tolerability 2, 1
• Once-daily dosing is superior to multiple daily doses because iron doses ≥60 mg stimulate hepcidin elevation that persists for 24 hours and blocks absorption of subsequent doses 1, 4

Optimal Administration Timing

Take ferrous gluconate in the morning on an empty stomach (1-2 hours before or after meals) with 250-500 mg of vitamin C to maximize absorption. 1, 3, 4

• Food consumed within 2 hours before or 1 hour after oral iron can reduce absorption by up to 50% 1, 3, 5
• Avoid tea and coffee within 1 hour of taking iron, as these are powerful inhibitors of iron absorption 1, 3, 4
• Avoid calcium-containing foods and aluminum-based antacids, which reduce iron absorption 3, 5, 4

Alternative Dosing for Tolerability

• If gastrointestinal side effects occur, consider alternate-day dosing (every other day), which significantly increases fractional iron absorption while reducing side effects 1, 4
• Taking with small amounts of food may improve tolerance, though it reduces absorption 1, 4
• Starting with a lower dose (1-2 tablets) and gradually increasing may improve tolerance 3, 5

Monitoring and Duration

• Check hemoglobin at 4 weeks to assess response; lack of at least 10 g/L rise after 2 weeks strongly predicts treatment failure 1, 4
• Continue treatment for approximately 3 months after hemoglobin normalizes to adequately replenish iron stores 1, 4
• Monitor blood counts every 6 months after completing therapy to detect recurrent iron deficiency 1, 4

Important Clinical Considerations

Ferrous gluconate is more expensive ($5.08/month) and less cost-effective than ferrous sulfate ($2.29/month) or ferrous fumarate ($1.63/month), with no proven advantage in efficacy or tolerability. 1, 5

• Ferrous sulfate and ferrous fumarate provide more elemental iron per tablet, requiring fewer pills to achieve target dosing 1, 3
• One study found ferrous preparations more effective than ferric preparations, with significantly greater hemoglobin increases 6

When to Consider Intravenous Iron

• If oral ferrous gluconate causes intolerable gastrointestinal symptoms despite dosing adjustments 1, 4
• If hemoglobin fails to rise after 2-4 weeks of adherent oral therapy 1, 4
• In patients with malabsorption, inflammatory bowel disease, chronic kidney disease, or when blood loss exceeds oral repletion capacity 1, 5, 4

Critical Pitfalls to Avoid

• Do not take multiple doses throughout the day, as this decreases total absorption due to hepcidin elevation 1, 4
• Do not use modified-release preparations, as they are less suitable for prescribing and may release iron beyond the duodenum where absorption is optimal 1
• Do not continue oral iron indefinitely in hemodialysis patients, as they require intravenous iron for adequate erythropoiesis 1, 5