Iron Preparations: Oral and IV Therapy for Iron Deficiency Anemia

This note reviews the major oral and IV iron preparations used to treat iron deficiency anemia, with a focus on administration, side effects, drug interactions, toxicity, and the patient teaching points most commonly tested on nursing exams.

Iron Preparations at a Glance

• Oral iron (ferrous salts) — ferrous sulfate, ferrous gluconate, ferrous fumarate. First-line therapy. Causes GI upset and dark stools. Best absorbed on an empty stomach with vitamin C.
• IV iron — ferric carboxymaltose, iron sucrose, iron dextran. Used when oral iron is not tolerated or absorption is impaired. Iron dextran has the highest allergy risk and requires a test dose.
• Iron polysaccharide complex (Niferex) — better tolerated than ferrous salts with fewer GI effects.

Oral Iron Preparations

• Oral iron is the first-line treatment for iron deficiency anemia.
• Ferrous sulfate is most commonly prescribed because it contains the highest amount of elemental iron per dose.
• Take on an empty stomach for optimal absorption; may take with food if GI upset occurs.
• Vitamin C or orange juice significantly enhances absorption.
• Every-other-day dosing improves fractional absorption and may reduce GI adverse effects compared to daily dosing.
• Liquid iron can stain teeth — mix with water and drink through a straw, then rinse the mouth.

Gastrointestinal Side Effects

• Common effects: nausea, vomiting, constipation, diarrhea, abdominal pain, epigastric discomfort.
• Counter constipation with increased fluids and fiber.
• Iron tablet gastropathy is an underdiagnosed condition in which oxidative stress causes mucosal inflammation and even mass formation in the stomach.
• Severe iron-induced gastropathy can cause bleeding requiring endoscopic intervention or partial gastrectomy.
• Taking iron with food reduces GI effects but also reduces absorption.

Dark Stools and Patient Teaching

• Iron causes harmless dark green or black stools — a normal expected effect.
• Teach patients to report red streaks, sharp abdominal pain, or cramps, which may indicate GI bleeding.
• Do not confuse iron-related black stools with melena.
• Discoloration resolves after therapy ends.

Other Oral Iron Side Effects

• Metallic taste from iron salts dissolving in the mouth; taking iron with food can reduce this.
• High-dose iron can reduce zinc absorption and lower serum zinc.
• Interacts with levodopa, levothyroxine, tetracyclines, and fluoroquinolones.

Drug Interactions

• Antacids, H2 blockers, PPIs — reduce iron absorption by decreasing stomach acid. Separate by 2–4 hours.
• Calcium supplements — compete with iron for absorption; take at different times.
• Levothyroxine — iron decreases its effectiveness; monitor thyroid levels and separate doses.
• Levodopa — iron reduces absorption; monitor for decreased effectiveness.
• Tetracyclines and fluoroquinolones — iron decreases antibiotic absorption; separate by 2–4 hours.
• Vitamin C — increases iron absorption (beneficial, but may worsen GI effects).
• Milk, tea, coffee, cereals — markedly reduce absorption; avoid co-administration.

IV Iron: Indications

• Used when oral iron is not tolerated, absorption is impaired, or rapid repletion is needed.
• Specific indications: chronic kidney disease (CKD), inflammatory bowel disease (IBD), cancer-related anemia, and patients needing major surgery on a short timeline.
• Also indicated in heart failure to improve exercise capacity and quality of life.
• In patients with inflammation, oral absorption is often impaired, making IV the preferred route.

IV Iron Administration and Safety

• Ferric carboxymaltose allows infusion of the total iron requirement in a single dose over 15–30 minutes.
• Iron sucrose is primarily used in hemodialysis patients and given in multiple smaller doses.
• Hypersensitivity reactions, including life-threatening anaphylaxis, can occur. Iron dextran carries the highest risk and requires a test dose.
• Extravasation can cause permanent brown skin staining; patients must report pain or irritation immediately.

Iron Toxicity and Overdose

• Acute iron overdose is a medical emergency, especially in children, and can cause multisystem organ failure, coma, and convulsions.
• Doses exceeding 60 mg/kg can be life-threatening.
• Antidote: deferoxamine.
• Signs of toxicity: severe vomiting, diarrhea, abdominal pain, lethargy, and metabolic acidosis.
• Hereditary hemochromatosis is an absolute contraindication — iron accumulation causes liver cirrhosis, liver cancer, and heart disease.

Monitoring Treatment Response

• Hemoglobin should rise by approximately 2 g/dL over 2–4 weeks.
• Once Hgb reaches the reference range, continue therapy for an additional 3 months to replenish iron stores.
• Evaluate patients on oral iron within 2–4 weeks of starting therapy.
• Monitor ferritin to assess iron stores and guide treatment duration.

Patient Teaching Points

• Take oral iron on an empty stomach with water or orange juice; with food only if GI upset occurs.
• Do not take with antacids, calcium, milk, tea, or coffee.
• Expect dark green or black stools — harmless — but report red stools, severe abdominal pain, or persistent vomiting.
• Use a straw for liquid iron and rinse the mouth to prevent tooth staining.
• Increase fluids and fiber to prevent constipation.
• Keep iron supplements out of reach of children — accidental overdose can be fatal.

Common Exam Traps

• Confusing iron-induced black stools with GI bleeding.
• Forgetting that iron is best absorbed on an empty stomach with vitamin C, not with milk or antacids.
• Administering iron at the same time as levothyroxine, levodopa, or antibiotics without separating doses.
• Not recognizing hypersensitivity risk with IV iron and the need for monitoring during infusion.
• Assuming daily dosing is always required — every-other-day dosing improves absorption and reduces side effects.
• Forgetting that ferritin is the key diagnostic marker for iron deficiency.

Key Takeaways

• Ferrous sulfate is first-line oral therapy; take on an empty stomach with vitamin C and separate from antacids, calcium, and milk by 2–4 hours.
• Expect dark/black stools; teach patients to report red stools or severe abdominal pain.
• IV iron (ferric carboxymaltose, iron sucrose, iron dextran) is used in CKD, IBD, heart failure, and intolerance to oral iron; iron dextran requires a test dose due to anaphylaxis risk.
• Deferoxamine is the antidote for acute iron toxicity; doses >60 mg/kg can be life-threatening, especially in children.
• Hemoglobin should rise ~2 g/dL in 2–4 weeks; continue therapy for 3 months after normalization to replenish stores.
• Hereditary hemochromatosis is an absolute contraindication to iron supplementation.