Oral Iron for Low GI Side Effects: Ferrous Sulfate 50-100mg Once Daily or Alternate-Day Dosing
For your patient with ferritin of 8 µg/L, prescribe ferrous sulfate 50-100 mg elemental iron once daily (or alternate-day dosing), taken in the morning on an empty stomach with 250-500 mg vitamin C to minimize gastrointestinal side effects while maintaining efficacy. 1, 2
Why This Dosing Strategy Minimizes GI Side Effects
Once-daily dosing is superior to multiple daily doses because increased dosing frequency elevates hepcidin for 24 hours, blocking subsequent iron absorption while significantly increasing side effects including constipation (which occurs in 12% of patients on standard dosing) 1, 2
Alternate-day (every-other-day) dosing is the preferred strategy if constipation becomes problematic, as this significantly increases fractional iron absorption and reduces gastrointestinal symptoms while maintaining therapeutic efficacy 1, 2
Lower doses (50-100 mg elemental iron) rather than higher doses improve tolerability without compromising effectiveness, as absorption plateaus at higher doses while side effects increase 1, 3
Optimal Timing and Administration
Take in the morning on an empty stomach (1-2 hours before meals) because serum hepcidin increases during the day and reduces absorption, making morning dosing superior to afternoon or evening administration 2
Co-administer with 500 mg vitamin C (ascorbic acid) to enhance absorption, especially if the patient needs to take iron with small amounts of food for tolerability 1, 2
If GI symptoms are intolerable on empty stomach, taking with small amounts of food may improve tolerability despite reducing absorption 1
What to Avoid
Avoid tea or coffee within 1 hour after taking iron, as these are powerful inhibitors reducing absorption by up to 54% 2
Avoid calcium-containing foods or supplements, fiber-rich foods, or antacids at the time of iron administration, as these significantly reduce iron absorption 2
Specific Formulation Recommendations
Start with standard ferrous sulfate (most cost-effective and well-studied) at 50-100 mg elemental iron once daily 1, 3
If ferrous sulfate is not tolerated, try ferrous gluconate or ferrous fumarate, as different formulations may be better tolerated in individual patients 1
Carbonyl iron-based products may cause GI irritation, constipation, diarrhea, nausea, vomiting, and abdominal pain, though adverse reactions are usually transient 4
Monitoring Response
Check hemoglobin at 4 weeks to assess response; expect a rise of at least 10 g/L within 2 weeks if oral iron is being absorbed 2
Repeat ferritin and complete blood count at 8-10 weeks to measure treatment success 3
When to Switch to Intravenous Iron
Consider IV iron if oral iron causes intolerable GI side effects despite dosing adjustments (switching to alternate-day dosing, taking with food, or trying different formulations) 1, 2
Switch to IV iron if hemoglobin fails to rise after 2-4 weeks of adherent oral therapy, indicating treatment failure 2
IV iron is preferred for patients with malabsorption conditions (celiac disease, inflammatory bowel disease, prior gastric surgery) where oral iron absorption is significantly impaired 2, 5
Common Pitfalls to Avoid
Don't prescribe multiple daily doses thinking it will speed up repletion—this only increases side effects without improving absorption 1, 2
Don't use excessive elemental iron content (>100 mg) as this reduces compliance due to increased GI side effects 3
Don't continue oral iron indefinitely without monitoring—repeat ferritin every 6-12 months once stores are repleted, as long-term daily supplementation with normal ferritin is potentially harmful 3