What is the maximum dose of ferrous sulfate (iron supplement)?

Maximum Dose of Ferrous Sulfate

The maximum recommended dose of ferrous sulfate for adults is 200 mg of elemental iron per day, which equates to approximately three 325 mg tablets of ferrous sulfate daily (as each tablet contains about 65 mg of elemental iron). 1

Dosing Recommendations

Adult Dosing

• Standard therapeutic dose: 200 mg of elemental iron daily, divided into 2-3 doses 1
• Equivalent in ferrous sulfate tablets: Three 325 mg tablets daily (each providing 65 mg elemental iron)
• Alternative dosing schedule: 100 mg elemental iron once daily for asymptomatic patients with mild anemia 2
• For severe anemia or symptomatic patients: 200 mg elemental iron daily 2

Pediatric Dosing

• 2-3 mg/kg/day of elemental iron 1

Administration Recommendations

• Take on an empty stomach (1 hour before or 2 hours after meals) to maximize absorption 3
• Avoid taking with coffee, tea, calcium supplements, or antacids 3
• Morning administration is preferable as afternoon/evening doses may be less effective due to circadian increases in hepcidin 4
• Consider alternate-day dosing to improve absorption and reduce side effects 4
  • Recent evidence suggests that doses ≥60 mg stimulate hepcidin, which inhibits absorption for 24 hours but subsides by 48 hours

Side Effects Management

• GI side effects (nausea, constipation, diarrhea) are common with oral iron and dose-dependent 1
• Side effect management options:
  • Reduce to once-daily dosing
  • Switch to alternate-day dosing 2, 4
  • Consider iron chelate formulations if intolerance persists 3

Monitoring Recommendations

• Check hemoglobin after 2 weeks of therapy to assess response 3
• For patients with resolved iron deficiency anemia:
  • Monitor every 3 months for at least a year 1
  • Then every 6-12 months thereafter 1

Special Considerations

• Higher doses do not necessarily improve absorption and may increase side effects 4
• For patients with inflammatory bowel disease, no more than 100 mg elemental iron per day is recommended 1
• Parenteral iron should be considered when:
  • Oral therapy is ineffective
  • Rapid correction is needed
  • Severe anemia is present
  • Patient has specific conditions like dialysis-dependent renal insufficiency, heart failure, or active IBD 2

Common Pitfalls

• Prescribing excessive doses beyond 200 mg elemental iron daily does not improve absorption and only increases side effects 1, 4
• Failing to recognize that food reduces iron absorption by up to 50% 3
• Continuing oral iron despite lack of response after 2 weeks (should consider IV iron instead) 3
• Not accounting for the difference between total tablet weight and elemental iron content (a 325 mg ferrous sulfate tablet contains only 65 mg of elemental iron) 1