Ferrous Gluconate

Ferrous gluconate is an oral ferrous iron salt with a low elemental iron content of about 12%, so a 300 mg tablet supplies about 35 mg of elemental iron. It is used for iron deficiency when other salts are not tolerated or available, and every dose here is written as elemental iron.

Classification. Haematinic; oral iron replacement.

Mechanism. Replenishes body iron for haem synthesis, myoglobin and iron-dependent enzymes through the same enterocyte transport route as other ferrous salts.

Pharmacokinetics. Absorption is about 10 to 20% and falls with raised hepcidin. Iron is stored as ferritin and has no regulated excretion.

Iron deficiency anaemia, adults.

• Dose: 65 to 105 mg elemental iron orally daily (two to three 300 mg tablets), as one dose or divided; alternate-day dosing is an option.
• Maximum: 200 mg elemental iron daily. Loading dose: none. Maintenance: the same dose.
• Duration: until haemoglobin is normal, then 3 months more.

Pregnancy.

• Prophylaxis: 30 to 60 mg elemental iron daily.
• Treatment: up to 200 mg elemental iron daily in divided doses.

Children.

• Treatment: 3 mg/kg of elemental iron daily, up to 6 mg/kg daily, maximum 200 mg daily.
• Prophylaxis: 1 to 2 mg/kg daily.

Adjustments. Kidney and liver: no adjustment; oral iron is poorly effective in advanced kidney disease and contraindicated in iron overload.

Contraindications. Haemochromatosis, iron overload, non-iron-deficiency anaemia, hypersensitivity.

Adverse effects. Gastrointestinal upset, constipation, diarrhoea, dark stools. The low elemental content means more tablets for the same iron dose, which can reduce adherence.

Boxed-warning-level risk. Iron overdose in children under 6 years can be fatal.

Interactions. Reduced absorption with proton pump inhibitors, antacids, calcium and tea. Iron reduces absorption of levothyroxine, quinolones, tetracyclines, levodopa, penicillamine, bisphosphonates and mycophenolate. Dolutegravir is given 2 hours before or 6 hours after iron, or with food.

Pregnancy and breastfeeding. Suitable in both.

Common errors. Under-dosing by treating the tablet count as the iron dose; failing to calculate elemental iron.

Administration. Take before food with water or fruit juice, or with food if not tolerated.

Monitoring. Haemoglobin at 2 to 4 weeks (rise of about 10 g/L) and at 3 months; ferritin once haemoglobin is normal, with deficiency under 30 µg/L.

Referral and escalation. Change to a higher-yield oral salt or to intravenous iron if there is intolerance or no response after 4 weeks of adherence. Ingestions above 20 mg/kg elemental iron need observation; above 60 mg/kg is an emergency.