How to Order Ferrous Sulfate for Anemia
Prescribe ferrous sulfate 200-325 mg (containing 65 mg elemental iron) once daily, taken on an empty stomach, and continue for approximately 3 months after hemoglobin normalizes to replenish iron stores. 1
Dosing Strategy
The most recent high-quality guidelines from the British Society of Gastroenterology (2021) recommend a paradigm shift from traditional multiple-daily-dosing to once-daily administration 1. This is based on evidence showing that oral doses of 60 mg elemental iron stimulate hepcidin levels, which reduces subsequent iron absorption by 35-45%. Consequently, 60 mg elemental iron once daily achieves similar overall absorption as 60 mg twice daily 1.
Standard Prescription:
- Ferrous sulfate 200-325 mg tablet once daily (provides 65 mg elemental iron per 200 mg tablet) 2
- Target dose: 50-100 mg elemental iron daily 1
- Timing: 30 minutes before meals on an empty stomach for optimal absorption 3
If Not Tolerated:
Switch to alternate-day dosing (one tablet every other day) rather than increasing frequency 1. Alternate-day administration actually increases fractional iron absorption compared to daily dosing, with similar efficacy but fewer gastrointestinal side effects 1.
Monitoring Protocol
Check hemoglobin at 2-4 weeks to assess response 1. Failure to achieve at least a 10 g/L rise in hemoglobin after 2 weeks strongly predicts subsequent treatment failure (sensitivity 90.1%, specificity 79.3%) 1.
Treatment Duration:
- Continue for approximately 3 months after hemoglobin normalizes to ensure adequate iron store repletion 1
- Monitor blood counts every 6 months initially after treatment completion to detect recurrent anemia 1
When to Use IV Iron Instead
Consider intravenous iron when oral iron is contraindicated, ineffective, or not tolerated 1. The 2024 AGA guidelines specifically recommend IV iron for 4:
- Impaired absorption: Post-bariatric surgery, active inflammatory bowel disease, celiac disease
- Ongoing blood loss exceeding oral absorption capacity
- Oral intolerance: Persistent gastrointestinal side effects despite alternate-day dosing
- Chronic inflammatory conditions: Chronic kidney disease, heart failure, cancer
For IV iron, formulations allowing 1-2 infusions are preferred (ferric carboxymaltose 750-1000 mg, ferric derisomaltose 1000 mg, or ferumoxytol 510-1020 mg) over multiple-dose regimens 4.
Common Pitfalls to Avoid
Dosing Errors:
- Don't prescribe multiple daily doses - this increases side effects without improving absorption 1
- Don't use modified-release preparations - they are less suitable for prescribing as iron may be released beyond the duodenum where absorption is optimal 1
Monitoring Failures:
- Don't wait longer than 4 weeks to check initial response - early non-responders need alternative therapy 1
- Don't stop treatment when hemoglobin normalizes - continue for 3 months to replenish stores 1
Side Effect Management:
Gastrointestinal side effects occur in nearly all patients on oral iron 5. If intolerable:
- First try alternate-day dosing (not lower daily doses split throughout the day)
- Then consider alternative oral formulations (ferrous fumarate, ferrous gluconate, or ferric maltol)
- Finally switch to IV iron if oral routes fail 1
Special Populations
Post-Bariatric Surgery:
Use IV iron preferentially - oral absorption is severely impaired due to duodenal bypass 4
Pregnancy (2nd/3rd trimester):
IV iron is indicated for more rapid repletion 6
Children:
Dose at 3 mg/kg/day of elemental iron (not to exceed adult dosing), given once daily 7. Ferrous sulfate is superior to iron polysaccharide complex for hemoglobin restoration 7.