What is the recommended ferrous sulfate dosing for an adult with iron‑deficiency anemia and for children aged 6 months to 12 years (e.g., a 20‑kg child)?

Ferrous Sulphate Dosing for Iron-Deficiency Anemia

For adults with iron-deficiency anemia, prescribe ferrous sulfate 200 mg once daily (providing 50-100 mg elemental iron), and for a 20-kg child aged 6 months to 12 years, prescribe 3 mg/kg/day of elemental iron (60 mg total for a 20-kg child), given once daily between meals.

Adult Dosing

The most recent British Society of Gastroenterology guidelines (2021) provide the clearest evidence-based recommendation for adults 1. The standard dose is 50-100 mg of elemental iron once daily, which translates to one ferrous sulfate 200 mg tablet (containing 65 mg elemental iron) taken once daily 1, 2.

Key Points for Adults:

• Once-daily dosing is now preferred over the traditional twice-daily regimen, as recent evidence shows alternate-day or once-daily dosing produces similar hemoglobin increments with significantly better tolerability 1
• The older recommendation of ferrous sulfate 200 mg twice daily (from 2011 guidelines) has been superseded by evidence showing lower doses are equally effective 3
• Take between meals on an empty stomach for optimal absorption, though taking with food is acceptable if gastrointestinal side effects occur 1
• Continue for 3 months after iron deficiency correction to replenish stores 3
• Expect hemoglobin to rise by at least 10 g/L within 2 weeks; failure to achieve this predicts non-response and warrants switching to intravenous iron 1

Important Caveats for Adults:

• Avoid tea and coffee within 1 hour of dosing, as they powerfully inhibit iron absorption 4
• If gastrointestinal side effects occur, consider lower doses (even 50 mg elemental iron on alternate days) rather than switching formulations immediately 1
• For patients intolerant to oral iron or with malabsorption (inflammatory bowel disease, post-bariatric surgery), proceed directly to intravenous iron 1, 4

Pediatric Dosing (6 Months to 12 Years)

Multiple guidelines converge on 3 mg/kg/day of elemental iron as the standard pediatric dose 5, 6.

For a 20-kg Child:

• Total daily dose: 60 mg elemental iron (3 mg/kg × 20 kg)
• Practical prescription: Ferrous sulfate drops or liquid formulation providing 60 mg elemental iron daily
• Administration: Once daily, between meals for optimal absorption 5

Dosing by Age/Weight Categories:

• Infants 6-23 months: 3 mg/kg/day, typically given as iron drops 5
• Children 2-12 years: 3 mg/kg/day, up to maximum of 60 mg elemental iron daily for school-age children 5
• Adolescent boys: Two 60-mg tablets daily (120 mg total) 5

Recent High-Quality Pediatric Evidence:

A 2017 randomized trial demonstrated that low-dose ferrous sulfate (3 mg/kg once daily) is superior to iron polysaccharide complex for treating pediatric IDA, with mean hemoglobin increasing from 7.9 to 11.9 g/dL over 12 weeks 7. This once-daily regimen achieved 29% complete resolution of IDA versus only 6% with iron polysaccharide complex (p=0.04) 7.

A 2020 study confirmed that 2 mg/kg/day of ferrous sulfate oral solution normalized hemoglobin in 95% of children aged 6-53 months within 3 months, with excellent tolerability 8. However, the standard 3 mg/kg/day remains the guideline-recommended dose 5.

Critical Pediatric Considerations:

• Monitor response at 4 weeks: Hemoglobin should increase by ≥1 g/dL or hematocrit by ≥3% 5
• Continue treatment for 2-3 months after correction to replenish stores 5
• Divided dosing (2-3 times daily) is mentioned in older guidelines 6, but recent evidence supports once-daily administration for better adherence 8, 7
• For children with gastrointestinal side effects, the dose can be reduced or given with food, though absorption decreases by up to 50% 6

Formulation Selection

Ferrous sulfate is the preferred first-line agent for both adults and children due to:

• Lowest cost (approximately $1-4.50 per month) 1, 6
• Highest elemental iron content per tablet (65 mg per 200 mg tablet) 1, 2
• Superior efficacy compared to iron polysaccharide complex in head-to-head trials 7
• Extensive safety and efficacy data across all age groups 1, 3

Alternative formulations (ferrous fumarate, ferrous gluconate) may be considered if ferrous sulfate is not tolerated, but they are not superior in efficacy 3.

When to Use Intravenous Iron

Switch to IV iron if:

• No hemoglobin rise of ≥10 g/L after 2 weeks of adherent oral therapy (adults) 1
• No hemoglobin rise of ≥1 g/dL after 4 weeks (children) 5
• Intolerable gastrointestinal side effects despite dose reduction
• Malabsorption conditions (inflammatory bowel disease, post-bariatric surgery, celiac disease) 1, 4
• Ongoing blood loss exceeding oral iron absorption capacity 1, 4

For IV iron in children, iron sucrose is the most studied and safest option, though not formally approved for pediatric use in Europe 9. Dosing is weight-based: 0.5-2 mg/kg per dose, with maximum single dose of 300 mg 9.