ferrous sulfate
iron supplement· Brands: Feosol, Slow-Fe, Ferro-Grad, PalaferPO
Mechanism of action
Iron is an essential component of haemoglobin, myoglobin, and various enzymes. Ferrous sulfate provides elemental iron in the ferrous (Fe2+) form, which is absorbed in the duodenum and proximal jejunum. Once absorbed, iron is bound to transferrin and transported to the bone marrow for erythropoiesis. The iron is incorporated into haemoglobin, allowing red blood cells to carry oxygen. It also replenishes iron stores as ferritin and haemosiderin. The therapeutic effect is to correct iron deficiency and its associated anaemia.
Pharmacokinetics
Ferrous sulfate is taken orally. Absorption occurs primarily in the duodenum and proximal jejunum. The ferrous form is better absorbed than ferric. Absorption is influenced by stomach acid, dietary factors (e.g., vitamin C enhances, tea and calcium reduce), and the body's iron status: absorption increases with iron deficiency. Iron is transported in the plasma bound to transferrin, and stored in the liver, spleen, and bone marrow as ferritin. Excretion is mainly via faeces, with small amounts lost in urine and sweat. There is no active elimination pathway, as iron is tightly regulated.
Indications & dosing
Iron deficiency anaemia
As ferrous sulfate; 325 mg provides 65 mg elemental iron.
- adult · PO: 325 mg TID · As ferrous sulfate; 325 mg provides 65 mg elemental iron.
Prophylaxis of iron deficiency
For pregnancy or chronic blood loss.
- adult · PO: 325 mg OD · For pregnancy or chronic blood loss.
Iron deficiency anaemia
Elemental iron dose; ferrous sulfate contains 20% elemental iron.
- pediatric · PO: 3–6 mg/kg/day divided · Elemental iron dose; ferrous sulfate contains 20% elemental iron.
Contraindications & precautions
- Haemochromatosis and other iron overload disorders · Excess iron accumulation can lead to organ damage.
- Known hypersensitivity to ferrous sulfate or any of its excipients · Rare but serious allergic reactions may occur.
- Conditions associated with iron overload (e.g., thalassaemia major, sideroblastic anaemia) unless concurrent iron deficiency is documented · Iron supplementation may exacerbate iron overload; use only if deficiency is proven.
- Active peptic ulcer disease or inflammatory bowel disease (e.g., ulcerative colitis, Crohn's disease) · Risk of worsening GI irritation; consider alternative routes or forms if needed.
- Take with food to minimise gastrointestinal irritation, ideally with a light meal or snack; avoid taking on an empty stomach.
- Avoid concurrent intake of tea, coffee, milk, antacids, or calcium supplements, as these reduce iron absorption; taking vitamin C (e.g., citrus fruit juice) may enhance absorption.
- Tablets must be kept out of reach of children, as accidental overdose can be fatal.
- Stools may darken during treatment; this is harmless but should be explained to the patient.
- Use with caution in patients with a history of gastrointestinal conditions such as peptic ulcer disease, ulcerative colitis, or Crohn's disease.
Adverse effects
- Dark stools
- Constipation
- Nausea
- Diarrhoea
- Abdominal pain or cramps
- Vomiting
- Allergic reactions (e.g., rash, pruritus)
- Anaphylaxisserious
- Iron overload (haemosiderosis) with long-term useserious
- Gastrointestinal bleedingserious
Interactions
- levothyroxinemoderateSeparate administration of levothyroxine and ferrous sulfate by at least 4 hours. Monitor serum TSH and free T4 levels, especially when starting or stopping iron therapy, and adjust the levothyroxine dose as needed. If separation is not feasible, consider alternative iron preparations or routes, and reassess thyroid function regularly.
Monitoring, pregnancy & toxicity
- Haemoglobin · Baseline, then after 4 weeks of therapy and periodically thereafter
- Ferritin · Baseline, then after 4 weeks of therapy
- Transferrin saturation · Baseline, then after 4 weeks of therapy
- GI symptoms (nausea, constipation, dark stools) · Throughout treatment
- Pregnancy: Ferrous sulfate is used for the prophylaxis and treatment of iron deficiency anaemia in pregnancy at recommended doses. It is considered safe in pregnancy when taken as recommended.
- Toxicity: GI toxicity: nausea, vomiting, abdominal pain, diarrhoea, haematemesis, melaena. · Supportive care, whole bowel irrigation; chelation with desferrioxamine for severe or systemic toxicity.
- Toxicity: Systemic toxicity: metabolic acidosis, lethargy, cardiovascular collapse, coma, seizures. · Intravenous desferrioxamine and intensive supportive care.
- Toxicity: Hepatotoxicity: hepatic necrosis in severe poisoning. · Supportive treatment and consider liver transplantation in fulminant failure.
Antidotes & reversal
- Deferoxamine · Chelation for significant toxicity (serum iron >500 mcg/dL, shock, or >60 mg/kg elemental iron).
Clinical notes
Ferrous sulfate is used to treat and prevent iron deficiency anaemia, including that due to chronic blood loss, pregnancy, or dietary insufficiency. It is usually given orally, with doses expressed in terms of elemental iron; ferrous sulfate contains about 20% elemental iron. Common adverse effects include gastrointestinal upset, constipation, and dark stools. To improve tolerance, it may be taken with food, but this reduces absorption. Iron supplements should be kept out of reach of children, as overdose is dangerous. Response is monitored by clinical improvement and blood tests (e.g., haemoglobin, ferritin). Caution in inflammatory bowel disease, haemochromatosis, and other iron overload states. Interactions: antacids, tetracyclines, and some other drugs reduce absorption. Always follow local guidelines and formulary.
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BNF; local formulary