What is the appropriate dosing regimen of iron bisglycinate for an adult woman with iron‑deficiency anemia due to heavy menstrual bleeding?

Iron Bisglycinate Dosing for Iron Deficiency Anemia with Heavy Menstrual Bleeding

For an adult woman with iron deficiency anemia due to heavy menstrual bleeding, take 50-100 mg of elemental iron once daily in the morning on an empty stomach, using standard ferrous sulfate as first-line therapy rather than iron bisglycinate, which lacks guideline support despite being marketed as better tolerated. 1

First-Line Iron Formulation

• Ferrous sulfate (200 mg tablet = 65 mg elemental iron) remains the gold standard and most cost-effective option at approximately £1.00 per 28-day supply. 1
• No oral iron formulation—including ferrous sulfate, ferrous fumarate, ferrous gluconate, or iron bisglycinate—has demonstrated superiority in efficacy or tolerability in guideline-level evidence. 1
• Alternative ferrous salts (ferrous fumarate 69-106 mg elemental iron or ferrous gluconate 37 mg elemental iron per tablet) may be substituted if ferrous sulfate is not tolerated, though evidence does not support improved tolerability with switching. 1, 2

Optimal Dosing Regimen

• Take a single morning dose of 50-100 mg elemental iron on an empty stomach to maximize absorption. 1, 2
• Once-daily dosing is superior to multiple daily doses because doses ≥60 mg trigger hepcidin elevation lasting approximately 24 hours, reducing absorption of subsequent doses by 35-45%. 1
• If standard daily dosing causes intolerable gastrointestinal side effects, switch to alternate-day dosing with 100-200 mg elemental iron, which markedly increases fractional iron absorption compared to daily dosing while lessening side effects. 1, 3

Iron Bisglycinate Considerations

While iron bisglycinate is marketed as having enhanced gastrointestinal tolerability 4, it is not recommended in major gastroenterology or hematology guidelines as a first-line agent. One small 2023 study found that 27 mg of liquid fermented iron bisglycinate improved serum ferritin without significant gastrointestinal distress in premenopausal women with iron deficiency without anemia 5, but this dose is below the 50-100 mg elemental iron recommended for treating iron deficiency anemia 1, 2. If you choose iron bisglycinate despite lack of guideline support, dose it at 50-100 mg elemental iron once daily to match evidence-based treatment targets. 1, 2

Monitoring Response

• Check hemoglobin at 2 weeks: failure to increase by at least 10 g/L strongly predicts treatment failure (sensitivity 90.1%, specificity 79.3%) and warrants investigation for non-compliance, continued bleeding, malabsorption, or concurrent B12/folate deficiency. 1, 2
• Monitor hemoglobin every 4 weeks until normalization, expecting approximately 1 g/dL increase within 2 weeks in responders. 1, 2
• Continue treatment for 3 months after hemoglobin normalizes to adequately replenish iron stores. 1, 2, 6

Strategies to Enhance Absorption

• Taking iron with 250-500 mg vitamin C enhances absorption by forming a chelate with iron. 1
• Avoid taking iron with tea, coffee, or calcium-containing foods/medications, which inhibit absorption. 1
• Taking iron on an empty stomach maximizes absorption but may increase gastrointestinal side effects; if intolerable, taking with food is acceptable despite reduced absorption. 1

When to Escalate to Parenteral Iron

Consider intravenous iron when: 1, 2

• Oral iron is not tolerated despite dosing modifications (alternate-day dosing, taking with food)
• Ferritin levels fail to improve after 4 weeks of adequate oral therapy
• Heavy menstrual bleeding continues uncontrolled, causing ongoing losses that exceed oral replacement capacity
• Conditions impairing oral iron absorption are present (inflammatory bowel disease, post-bariatric surgery)

Intravenous iron produces clinically meaningful hemoglobin response within one week and can replenish total body iron stores in one or two infusions of 500-1000 mg using modern formulations like ferric carboxymaltose or ferric derisomaltose. 1

Common Pitfalls to Avoid

• Do not prescribe modified-release iron preparations, which show uniformly low absorption and are designated "less suitable for prescribing" by the British National Formulary. 1
• Do not rely on multivitamin preparations containing ≤14 mg elemental iron, which are insufficient for treating iron deficiency anemia. 1
• Do not prescribe multiple daily doses expecting better results; this only increases side effects without improving absorption due to hepcidin-mediated blockade. 1
• Do not stop treatment when hemoglobin normalizes; continue for 3 additional months to replenish iron stores. 1, 2, 6