Aluminium hydroxide !

A non-absorbed antacid that neutralises stomach acid and causes constipation. It binds phosphate, and its aluminium builds up in kidney failure.

Updated 2026-11-01

Class: Antacids
Target: Gastric acid (H⁺) in the stomach lumen
ATC code: A02AB01

Also called: Aluminum hydroxide (US spelling), Algeldrate

Mechanism of action

Aluminium hydroxide reacts slowly with hydrochloric acid to form aluminium chloride and water, raising gastric pH and lowering pepsin activity. It is poorly absorbed. In the intestine aluminium binds phosphate into insoluble salts, which lowers phosphate absorption, and it slows bowel transit.

Aluminium hydroxide neutralises acid in the stomach
Gastric pH rises and pepsin works less
In the gut, aluminium binds dietary phosphate
Bowel transit slows: constipation

Pharmacokinetics

Absorption: Poorly absorbed; small amounts of aluminium do enter the blood.
Elimination: Mostly in the faeces; absorbed aluminium is excreted by the kidney, which fails in chronic kidney disease.

Indications

Heartburn, acid indigestion and upset stomach, often combined with magnesium hydroxide. Gastro-oesophageal reflux disease (GERD) →
Symptom relief in peptic ulcer, gastritis and oesophagitis. Peptic ulcer disease →

Adverse effects

Common

Constipation
Chalky taste

Contraindications

Allergy to aluminium hydroxide

Key interactions

Tetracyclines, digoxin, iron: Lower absorption of these drugs.
Aspirin, iron salts and multivitamins: Possible interactions listed for aluminium–magnesium antacids; they are spaced apart.
Sucralfate: More total aluminium in the body, a concern in kidney failure.

What is monitored

Phosphate with long-term use
Kidney function, and signs of aluminium toxicity in kidney failure
Bowel habit

Administration and safety

Oral liquid or tablets; the liquid is shaken before use
Other medicines are separated from it, and the label asks for advice when taking prescription drugs
It is not used at the maximum dosage for more than two weeks without medical review

Nursing care

Ask about constipation; combining with magnesium can offset it
Space other oral medicines away from the antacid
In kidney disease, check that its use has been reviewed by the treating team
Teach the patient that symptoms lasting more than two weeks need evaluation

Pregnancy and breastfeeding

The patient leaflet asks pregnant or breastfeeding women to discuss its use with their doctor.

Test yourself

Think of the answer, then tap the question to see it.

Which gut effect does aluminium hydroxide have, and how is it often balanced?

Constipation; it is combined with magnesium hydroxide, which loosens the stool.

Which electrolyte can fall with long-term aluminium hydroxide, and why?

Phosphate, because aluminium binds dietary phosphate in the gut.

Why is aluminium a concern in patients on dialysis?

Absorbed aluminium cannot be cleared by the kidney or by dialysis and builds up in bone and brain.

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Educational content on how drugs work; not a prescribing guide and no substitute for a health professional's advice. No doses are given.

Sources: DailyMed - ALUMINUM HYDROXIDE liquid (DailyMed (U.S. National Library of Medicine), 2025); Medications for the Treatment of Gastric Acidity - Gastroenterology - MSD Manual Professional Edition (MSD Manual Professional Edition, 2025); Aluminum Hydroxide and Magnesium Hydroxide: MedlinePlus Drug Information (MedlinePlus (U.S. National Library of Medicine), 2023); DailyMed - SUCRALFATE tablet (DailyMed (U.S. National Library of Medicine), 2026).

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