Ferrous Sulfate Has Better Absorption Than Ferrous Gluconate
Ferrous sulfate is better absorbed than ferrous gluconate, providing nearly twice the elemental iron per tablet (65mg vs 35mg) with similar bioavailability profiles. 1
Comparison of Iron Preparations
Iron supplementation is commonly prescribed for iron deficiency anemia, with several oral formulations available. When comparing absorption:
| Iron Preparation | Elemental Iron Content | Relative Absorption |
|---|---|---|
| Ferrous sulfate | 65mg per 325mg tablet | Reference standard |
| Ferrous gluconate | 35mg per 325mg tablet | Similar bioavailability per mg |
| Ferrous fumarate | 108mg per 325mg tablet | Similar bioavailability per mg |
Factors Affecting Absorption
The absorption of oral iron preparations is influenced by several factors:
- Elemental iron content: Ferrous sulfate provides nearly twice the elemental iron per tablet compared to ferrous gluconate (65mg vs 35mg) 1
- Bioavailability: The bioavailability per mg of elemental iron is similar between ferrous sulfate and ferrous gluconate
- Gastric acidity: Iron absorption is enhanced in acidic environments
- Timing of administration: Iron is best absorbed when taken on an empty stomach
- Food interactions: Food can reduce iron absorption by up to 50% when taken within 2 hours before or 1 hour after meals 1
Clinical Evidence
While both preparations are effective, ferrous sulfate is generally preferred due to:
- Higher elemental iron content per tablet (65mg vs 35mg) 1
- Lower cost ($2.29 vs $5.08 monthly for equivalent doses) 1
- More efficient iron loading due to higher elemental iron content
In peritoneal dialysis patients, one study found that ferrous gluconate was better absorbed and tolerated than ferrous sulfate when administered in high doses 2. However, this represents a specific patient population and administration protocol rather than general use.
Practical Considerations
When prescribing iron supplements:
- Standard dosing: 50-100mg elemental iron once daily is recommended for iron deficiency anemia 1, 3
- Administration: Best taken on an empty stomach in the morning to maximize absorption 3
- Duration: Treatment should continue for 3 months after hemoglobin normalization to replenish iron stores 3
- Monitoring: Check hemoglobin levels within 4 weeks of starting therapy; an Hb rise of at least 10 g/L after 2 weeks predicts successful treatment 1, 3
Common Pitfalls to Avoid
- Inadequate dosing: Ensure sufficient elemental iron content (50-100mg daily)
- Premature discontinuation: Continue treatment for 3 months after hemoglobin normalization
- Ignoring side effects: Gastrointestinal side effects may reduce compliance; consider alternate-day dosing if needed
- Overlooking absorption factors: Advise taking iron supplements on an empty stomach, away from medications that reduce absorption (antacids, calcium supplements)
In conclusion, while both ferrous sulfate and ferrous gluconate are effective iron supplements, ferrous sulfate is generally preferred due to its higher elemental iron content per tablet, lower cost, and established efficacy in treating iron deficiency anemia.