Side Effects of Maalox (Aluminum Hydroxide, Magnesium Hydroxide, Simethicone)
Maalox is generally well-tolerated with minimal side effects when used short-term as directed, but chronic high-dose use can lead to serious complications including phosphate depletion, osteomalacia, and electrolyte disturbances, particularly in patients with renal impairment. 1
Common Side Effects
Gastrointestinal Effects:
- Diarrhea (primarily from magnesium hydroxide component) is the most frequent side effect 2, 3
- Constipation can occur, particularly with aluminum-containing formulations 2
- Abdominal pain, nausea, and vomiting may develop 2
- These gastrointestinal disturbances are typically mild and dose-dependent 4, 3
Serious Side Effects with Chronic Use
Phosphate Depletion Syndrome:
- Aluminum and magnesium hydroxide bind phosphate in the gut, causing malabsorption 4, 5
- Chronic use can lead to severe hypophosphatemia, even in patients with normal renal function 5, 6
- This results in osteomalacia with skeletal demineralization, bone pain, muscle weakness, and pathologic fractures 5, 6
- One case documented severe osteomalacia after consuming 18 kg of elemental aluminum over 8 years, despite normal renal function 5
Electrolyte and Metabolic Disturbances:
- Metabolic alkalosis can develop, particularly with high doses 4
- Elevated urinary pH favors precipitation of calcium and magnesium salts, predisposing to renal stone formation 4
- Fluid retention may occur depending on sodium content of the preparation 4
Aluminum and Magnesium Toxicity:
- In patients with renal insufficiency (creatinine clearance <20 mL/min), aluminum and magnesium can accumulate to toxic levels rapidly 2, 1, 4
- Aluminum deposition in brain gray matter can contribute to dialysis encephalopathy syndrome in renal failure patients 4
- Even with normal renal function, chronic high-dose use can cause aluminum accumulation along bone surfaces (27.6% of bone surface in one documented case) 5
- Hypermagnesemia risk increases substantially in renal impairment 2, 1
Drug Interactions
Reduced Absorption of Other Medications:
- Antacids containing aluminum and magnesium significantly reduce absorption of fluoroquinolones (e.g., rufloxacin bioavailability decreased to 64% when taken 5 minutes after antacid) 7
- Tetracyclines (doxycycline) have reduced absorption when taken with aluminum, calcium, or magnesium-containing antacids 2
- Azithromycin should not be administered with aluminum- and magnesium-containing antacids 2
Warning Signs Requiring Medical Attention
Stop use and seek medical care if: 1
- Rectal bleeding occurs
- No bowel movement after use (may indicate serious condition)
- Laxative effect needed for more than 1 week
- Sudden change in bowel habits lasting over 14 days
High-Risk Populations
Contraindications and Precautions:
- Kidney disease patients: Avoid use entirely if creatinine clearance <20 mL/min due to hypermagnesemia and aluminum toxicity risk 2, 1
- Magnesium-restricted diet: Consult physician before use 1
- Pregnancy and breastfeeding: Consult healthcare professional before use 1
- Chronic users: Even within label recommendations, long-term maximum-dose use can cause severe complications 5
Clinical Pearls
- Short-term use (less than 1-2 weeks) consistent with manufacturer's directions is safe for most patients with normal renal function 5
- Patients should take other medications at least 2-4 hours apart from Maalox to avoid absorption interference 7
- Monitor phosphate, calcium, magnesium, and aluminum levels in patients requiring chronic therapy 5, 6
- The clinical syndrome of phosphate depletion and osteomalacia is reversible with antacid withdrawal and phosphate/calcium/vitamin D supplementation 5, 6