Aluminium and Magnesium Antacids

💊 Key point: Magnesium-containing antacids tend to be laxative, whereas aluminium-containing antacids are more often constipating. Combined magnesium + aluminium formulations balance out these colonic side-effects.

📖 About

Always check the BNF (or equivalent local formulary) for prescribing guidance on antacids.

• Primarily used for short-term relief of dyspepsia, GORD, and indigestion.
• Generally safe but can interact with other drugs by altering gastric pH or binding them in the gut.

⚙️ Mode of Action

• Neutralises gastric hydrochloric acid → symptom relief in dyspepsia/heartburn.
• Aluminium hydroxide also binds dietary phosphate, reducing phosphate absorption (used in CKD with hyperphosphataemia).

📋 Indications

• 🌡️ Dyspepsia, GORD, heartburn.
• 🔗 Hyperphosphataemia in CKD (phosphate-binding effect).
• Adjunct in peptic ulcer disease (less common with modern PPIs/H₂ blockers).

💊 Common Preparations & Doses (BNF examples)

• Aluminium Hydroxide 500 mg tablets QDS (often with added laxative to offset constipation).
• Aluminium Hydroxide 475 mg capsules (same considerations as tablets).
• Magnesium Carbonate mixture 10 mL TDS with water.
• Magnesium Trisilicate 1–2 tablets PRN (traditional “chalky” antacid).
• Combination: Magnesium Trisilicate + Magnesium Carbonate + Sodium Bicarbonate, 10–20 mL TDS.

🔄 Interactions

• Can reduce absorption of drugs such as tetracyclines, fluoroquinolones, iron, and levothyroxine.
• Separate administration by at least 2 hours from other medications.
• See BNF for full interaction list.

⛔ Contraindications

• ⚠️ Hypophosphataemia.
• ⚠️ Advanced CKD on haemodialysis (risk of aluminium accumulation and toxicity).

⚠️ Side Effects

• 💨 Constipation (especially with aluminium).
• 💩 Diarrhoea (especially with magnesium).
• 🧠 Aluminium accumulation in renal failure → risk of osteomalacia and dementia-like symptoms (rare in modern practice with monitoring).
• ⬇️ Hypophosphataemia (especially with chronic aluminium use).
• Rarely: acute porphyria precipitation.

📚 References

• BNF: Antacids
• NICE Clinical Knowledge Summaries: Dyspepsia & GORD