Starting Ferrous Sulfate for Iron Deficiency Anemia
Start with one tablet of ferrous sulfate 200 mg (65 mg elemental iron) once daily, taken on an empty stomach. 1
Initial Dosing Regimen
The British Society of Gastroenterology 2021 guidelines provide clear direction: commence oral iron replacement therapy once daily with 50-100 mg elemental iron 1. A standard ferrous sulfate 200 mg tablet contains 65 mg of elemental iron 2, making it the ideal starting formulation.
Key Dosing Principles
Once daily dosing is optimal because oral iron stimulates hepcidin levels that remain elevated for up to 48 hours, blocking further iron absorption 3. Taking iron more than once daily does not improve absorption but increases gastrointestinal side effects.
Take on an empty stomach for maximum absorption, though patients who cannot tolerate this may take it with meals 3
Avoid tea and coffee within one hour of taking iron, as these are powerful inhibitors of absorption 3
Monitoring and Response Expectations
Check hemoglobin at 2 weeks: You should see an increase of at least 10 g/L (1 g/dL). Failure to achieve this rise has 90.1% sensitivity and 79.3% specificity for predicting subsequent treatment failure 1. This is your critical decision point.
Recheck at 4 weeks to confirm ongoing response, then continue treatment for approximately 3 months after hemoglobin normalizes to replenish iron stores 1.
If Not Tolerated: Alternative Strategies
When gastrointestinal side effects occur (constipation 12%, diarrhea 8%, nausea 11% 3):
Reduce to alternate-day dosing (one tablet every other day) - this maintains similar overall efficacy with significantly fewer side effects 1
Consider ferric maltol 30 mg twice daily if patient has inflammatory bowel disease or previous intolerance to traditional iron salts 1
Switch to intravenous iron if oral iron is contraindicated, ineffective, or not tolerated 1
Common Pitfalls to Avoid
Do not prescribe twice-daily or three-times-daily dosing - this outdated approach increases side effects without improving absorption due to hepcidin-mediated blockade 3. The 2024 AGA guidelines explicitly state there is "no reason to take iron more than once a day" 3.
Do not use modified-release preparations - these are indicated as "less suitable for prescribing" in the British National Formulary 1 because iron is released beyond the duodenum where absorption is optimal.
Do not delay treatment awaiting investigations unless colonoscopy is imminent 1
When to Escalate to IV Iron
Consider intravenous iron when 3:
- Hemoglobin fails to increase by 1 g/dL within 2 weeks
- Ferritin does not increase within one month despite adherence
- Patient has malabsorption (post-bariatric surgery, active inflammatory bowel disease, celiac disease)
- Ongoing blood loss exceeds oral iron absorption capacity
Practical Administration Tips
Adding 500 mg vitamin C (ascorbic acid) may enhance absorption, particularly if taken with meals 3. Taking iron with meat protein also improves absorption 3.
The cost-effectiveness of ferrous sulfate (approximately £1.00-2.50 per 28 days 1) makes it the preferred first-line agent over more expensive alternatives like ferric maltol (£47.60 per 28 days 1).