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
