Ferrous Sulfate Dosing for Iron Deficiency Anemia
The prescribed regimen of ferrous sulfate 325 mg three times weekly for 30 days is inadequate for treating iron deficiency anemia and should be changed to once-daily dosing for at least 2-3 months after hemoglobin normalization. 1
Correct Dosing Regimen
Standard treatment requires ferrous sulfate 325 mg (65 mg elemental iron) once daily, not three times weekly. 1, 2 The FDA-approved dosing is 2-3 times daily, though recent evidence supports once-daily dosing as equally effective with better tolerability 2, 3.
- Once-daily dosing (325 mg) is as effective as divided dosing and results in better iron absorption due to lower hepcidin elevation 3
- Alternate-day dosing (every other day) actually increases fractional iron absorption by 21.8% compared to 16.3% with consecutive daily dosing, though this may prolong treatment duration 3
- Three times weekly dosing has no evidence base and will result in treatment failure 1
Duration of Treatment
Treatment must continue for 2-3 months after hemoglobin normalization to replenish iron stores, making the 30-day prescription insufficient. 1
- Hemoglobin should be checked within 4 weeks of starting treatment to assess response 1
- Absence of hemoglobin rise ≥10 g/L after 2 weeks predicts treatment failure (sensitivity 90.1%, specificity 79.3%) 1
- After successful correction, monitor every 3 months for at least one year to detect recurrence 4, 1
Optimizing Absorption and Tolerability
Take iron on an empty stomach (1 hour before or 2 hours after meals) to maximize absorption, though this increases gastrointestinal side effects. 1
- Co-administration with vitamin C (250-500 mg) enhances absorption 1
- Avoid taking with tea, coffee, or calcium-containing foods/supplements, which inhibit absorption 1
- If gastrointestinal side effects occur (heartburn, abdominal pain, black stools are most discriminating), consider alternate-day dosing rather than stopping treatment 5, 3
When the Prescribed Regimen Fails
If standard oral iron therapy fails or is not tolerated, intravenous iron should be considered. 1, 6
Intravenous iron is specifically indicated for:
- Oral iron intolerance despite dosing modifications 1, 6
- Malabsorption conditions (celiac disease, post-bariatric surgery, inflammatory bowel disease) 4, 1, 6
- Chronic inflammatory conditions (chronic kidney disease, heart failure, cancer) 6
- Ongoing blood loss 6
- Second and third trimesters of pregnancy 6
Critical Pitfalls to Avoid
The three most common errors in iron deficiency treatment are inadequate dosing frequency, insufficient duration, and failure to monitor response. 1
- Three times weekly dosing is a prescribing error - no guideline or evidence supports this frequency 1
- 30 days is too short - treatment requires months, not weeks 1
- Failure to recheck hemoglobin within 4 weeks misses early treatment failure 1
- Stopping treatment when hemoglobin normalizes without replenishing stores (requires additional 2-3 months) 1
Monitoring Parameters
Check hemoglobin within 4 weeks, then continue treatment for 2-3 months after normalization. 1
- If no response after 2 weeks (hemoglobin rise <10 g/L), investigate for non-compliance, ongoing blood loss, malabsorption, or incorrect diagnosis 1
- Target ferritin >100 μg/L to prevent rapid recurrence 4
- In inflammatory bowel disease patients, aim for ferritin up to 400 μg/L to prevent recurrence within 1-5 years 4