What is the treatment plan for an adult with iron deficiency anemia taking ferrous fumarate 300 mg?

Treatment Plan for Iron Deficiency Anemia with Ferrous Fumarate 300 mg

Start with one tablet of ferrous fumarate 300 mg (containing approximately 100 mg elemental iron) once daily, taken on an empty stomach, as this dosing provides optimal efficacy while minimizing gastrointestinal side effects. 1, 2, 3

Initial Dosing Strategy

• Prescribe ferrous fumarate 300 mg (approximately 100 mg elemental iron) once daily as the standard initial regimen for uncomplicated iron deficiency anemia 1, 2, 3
• Take the tablet on an empty stomach to maximize absorption, ideally 1-2 hours before meals 3
• If gastrointestinal side effects occur (nausea, constipation, abdominal discomfort), reduce to one tablet every other day rather than discontinuing therapy, as alternate-day dosing maintains efficacy with significantly better tolerability 2, 3
• Consider taking with citrus fruits/drinks or vitamin C to enhance absorption, but separate calcium supplements by 1-2 hours to avoid interference 1

Monitoring Response

• Check hemoglobin at 2 weeks: absence of at least 10 g/L rise predicts treatment failure with 90% sensitivity and should prompt investigation for malabsorption, ongoing blood loss, or inflammatory conditions 3
• Recheck hemoglobin every 4 weeks until normalized 2, 3
• Typical response shows hemoglobin improvement of approximately 2 g/dL within 3-4 weeks of oral therapy 1

Duration of Treatment

• Continue oral iron for 2-3 months after hemoglobin normalization to adequately replenish bone marrow iron stores 1, 2, 3
• After completing the initial treatment course, monitor hemoglobin and mean corpuscular volume (MCV) at 3-month intervals for one year, then annually 1
• Additional oral iron should be given if hemoglobin or MCV falls below normal on follow-up 1

When to Switch to Intravenous Iron

Consider intravenous iron if any of the following conditions are present:

• No hemoglobin rise of at least 10 g/L after 2 weeks of oral therapy 3
• Intolerance to at least two different oral iron preparations despite alternate-day dosing 1, 2
• Active inflammatory conditions (elevated CRP >4 mg/L, inflammatory bowel disease, chronic heart failure) where oral absorption is impaired by hepcidin-mediated blockade 2, 3
• Ongoing blood loss that exceeds oral replacement capacity 3
• Malabsorption syndromes (celiac disease, post-bariatric surgery, inflammatory bowel disease with active inflammation) 3
• Severe anemia with hemoglobin <10 g/dL requiring rapid correction 3

Special Population Considerations

For patients with inflammatory conditions (CRP >4 mg/L):

• Ferritin levels up to 100 μg/L may still indicate true iron deficiency due to acute-phase reactant properties 1, 2, 3
• Intravenous iron should be first-line therapy rather than oral iron, as inflammation blocks intestinal iron absorption regardless of dose 3

For elderly patients with comorbidities:

• Carefully weigh risks versus benefits of invasive gastrointestinal investigations to identify bleeding sources 1, 2
• Consider CT colonography as an alternative to colonoscopy in those unsuitable for invasive procedures 1, 2
• Recognize that anemia of chronic disease can mimic iron deficiency anemia, with only 11% of suspected cases having confirmed iron deficiency 1, 2

For patients with inflammatory bowel disease:

• Oral iron should contain no more than 100 mg elemental iron daily 1
• Intravenous iron is preferred for moderate to severe anemia (Hb <100 g/L) or active disease, as it has an odds ratio of 1.57 for achieving hemoglobin increase compared to oral iron 1, 3

Critical Pitfalls to Avoid

• Do not prescribe higher doses (e.g., 200 mg three times daily): 100 mg elemental iron daily is as effective as higher doses with significantly fewer side effects 2, 3, 4
• Do not defer iron replacement while awaiting investigations unless colonoscopy is imminent, as delaying treatment worsens outcomes 1, 3
• Do not assume dietary deficiency as the primary cause in adults, particularly men and postmenopausal women, as gastrointestinal blood loss and chronic disease are far more common 2
• Do not interpret ferritin 30-100 μg/L as "adequate" when CRP is elevated, as this may still represent true iron deficiency 3
• Do not continue oral iron indefinitely without response: if hemoglobin fails to rise after 4 weeks, investigate for malabsorption, ongoing blood loss, or switch to intravenous iron 1, 2

Blood Transfusion Considerations

• Transfusion is rarely required and should be reserved for severe symptomatic anemia with circulatory compromise 3
• Target hemoglobin 70-90 g/L if transfusion is necessary 3
• Iron replacement therapy must still follow transfusion, as each unit of blood contains only approximately 200 mg elemental iron, insufficient to replenish stores 3