Iron tablet dose
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iron tablet dose elemental iron deficiency anemia WHO guidelines 2025
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Here is a complete, evidence-based summary of iron tablet dosing:
Iron Tablet Dosing
Common Oral Iron Preparations
| Preparation | Typical Single Dose | Elemental Iron |
|---|---|---|
| Ferrous sulfate | 325 mg | 65 mg |
| Ferrous gluconate | 325 mg | 35 mg |
| Iron bisglycinate | 25 mg tablet | 25 mg |
| Polysaccharide-iron complex | 150 mg | 150 mg |
- Goldman-Cecil Medicine, Table 145-4
Therapeutic Doses (Iron Deficiency Anemia)
Adults:
- 60-110 mg elemental iron per day (Lancet 2025 guidelines) - once daily dosing preferred
- Old teaching was 150-200 mg/day, but current evidence supports lower doses with better tolerability
- Give as a single morning dose - do NOT give more than once daily (a second dose is absorbed ~35-45% less due to hepcidin rise after the first dose)
Children (Harriet Lane, 23rd ed.):
| Age group | Dose |
|---|---|
| Premature infant | 2 mg elemental Fe/kg/day; max 15 mg/day |
| Full-term infant | 1-2 mg elemental Fe/kg/day; max 15 mg/day |
| Child 2-12 yr | 2 mg elemental Fe/kg/day; max 30 mg/day |
| Adolescent / Adult | 60 mg elemental Fe/day once daily |
Pregnancy/Prophylaxis:
- 30-60 mg elemental iron/day
Key Practical Points
- Once daily max - giving iron twice daily is not more effective and increases GI side effects
- Alternate-day dosing - every-other-day iron is an acceptable alternative if daily dosing causes GI upset (nausea, constipation, epigastric pain); the 2025 Lancet guidelines support this for adults
- Vitamin C - take 200 mg vitamin C per 30 mg of iron to enhance absorption
- Avoid with: antacids, tea, milk/dairy, tetracyclines, calcium (all reduce absorption)
- Empty stomach preferred for absorption, but food reduces GI side effects
- Duration: treat for at least 3 months after hemoglobin normalizes to replenish iron stores
When to Switch to IV Iron
- No Hb response within 2 weeks of oral iron
- Unable to tolerate oral iron
- Malabsorption (celiac disease, bowel surgery, bariatric procedures, IBD)
- Ongoing blood loss too great for oral replacement
- Pregnancy with significant deficiency
- Goldman-Cecil Medicine
Ferrous sulphate dosage for adults
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ferrous sulfate dosage adults iron deficiency anemia 2024 2025
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Ferrous Sulfate Dosage for Adults
Available Formulations
| Form | Tablet Size | Elemental Iron |
|---|---|---|
| Ferrous sulfate (hydrated) | 325 mg | 65 mg |
| Ferrous sulfate (desiccated) | 200 mg | 65 mg |
| Extended-release | 160 mg | ~50 mg |
Dosing by Indication
| Indication | Dose | Elemental Iron Delivered |
|---|---|---|
| Iron deficiency anemia (treatment) | 325 mg once daily (preferred) | 65 mg/day |
| Traditional regimen | 325 mg 2-4 tablets/day | 130-260 mg/day |
| Extended-release | 160 mg once or twice daily | ~50-100 mg/day |
| Prophylaxis / supplementation | 325 mg once daily or on alternate days | 65 mg/day |
| Pregnancy | 15-30 mg elemental iron/day | - |
| Rapid repletion (active bleeding) | Up to 120 mg elemental iron 4x/day | 480 mg/day |
Key Dosing Principle (Modern Evidence)
The old standard of 325 mg three times daily has been updated. Current evidence and guidelines (Goodman & Gilman's, 16e) recommend:
Ferrous sulfate 325 mg once daily on an empty stomach - this maximizes absorption while minimizing GI side effects.
Why once daily works better:
-
After a morning dose, serum iron rises and stimulates hepcidin release
-
Hepcidin suppresses iron absorption for up to 48 hours
-
A second dose on the same day is absorbed 35-45% less than the first
-
Alternate-day dosing is an equally valid option for patients with GI intolerance
-
Goodman & Gilman's Pharmacological Basis of Therapeutics; Katzung's Basic & Clinical Pharmacology, 16th ed.
Hemoglobin Response to Treatment
| Total iron dose (mg/day) | Absorption (%) | Iron absorbed (mg) | Hb rise (g/L/day) |
|---|---|---|---|
| 35 | 40% | 14 mg | 0.7 |
| 105 | 24% | 25 mg | 1.4 |
| 195 | 18% | 35 mg | 1.9 |
| 390 | 12% | 45 mg | 2.2 |
Note: Higher doses don't proportionally improve outcomes - absorption % falls as dose rises.
- Goodman & Gilman's, Table 45-5
Practical Tips
- Duration: Continue for 3-6 months after Hb normalizes to replenish stores - Katzung's
- With food: Reduces GI side effects (nausea, cramps, constipation) but decreases absorption
- Empty stomach: Best absorption, but may cause more GI upset
- Vitamin C (200 mg per 30 mg iron): Enhances absorption
- Avoid: Antacids, dairy, tea, tetracyclines, calcium supplements - all reduce absorption
- Black stools: Expected, not clinically significant (but can mask GI bleeding)
- Switch to IV if no Hb response within 2 weeks, or if GI intolerance persists
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