ALUMINUM HYDROXIDE AND MAGNESIUM TRISILICATE
Clinical safety rating: caution
Comprehensive clinical and safety monograph for ALUMINUM HYDROXIDE AND MAGNESIUM TRISILICATE (ALUMINUM HYDROXIDE AND MAGNESIUM TRISILICATE).
Aluminum hydroxide and magnesium trisilicate act as antacids by neutralizing gastric hydrochloric acid, increasing gastric pH, and inhibiting pepsin activity. Aluminum hydroxide forms aluminum phosphate in the intestine. Magnesium trisilicate reacts with HCl to form magnesium chloride and silicic acid, which may provide additional protective coating.
| Metabolism | Aluminum hydroxide: Primarily excreted unchanged in feces; minimal absorption. Magnesium trisilicate: Magnesium ions are partially absorbed; silicic acid is excreted renally. No significant hepatic metabolism. |
| Excretion | Aluminum and magnesium ions are minimally absorbed. Absorbed aluminum is primarily excreted renally (elimination half-life prolonged in renal impairment); unabsorbed components are eliminated in feces. Magnesium trisilicate may dissociate; absorbed magnesium is excreted renally. Fecal elimination accounts for >95% of the dose. |
| Half-life | Aluminum: terminal half-life in patients with normal renal function is approximately 8 hours for absorbed fraction, but may extend to days in renal failure. Magnesium: half-life of absorbed magnesium is 4-6 hours. Clinical context: accumulation risk in chronic kidney disease. |
| Protein binding | Aluminum: approximately 50-70% bound to albumin and transferrin. Magnesium: approximately 30% bound to albumin. |
| Volume of Distribution | Aluminum: Vd ~0.2-0.5 L/kg, indicating distribution primarily into extracellular fluid. Magnesium: Vd ~0.3-0.4 L/kg, primarily extracellular. Clinical meaning: limited tissue penetration; prolonged retention in bone. |
| Bioavailability | Oral: systemic absorption of aluminum <1% under normal conditions; magnesium absorption ~15-30%. Bioavailability increases with concomitant citrate or vitamin D. Rectal: not applicable. |
| Onset of Action | Oral: onset of acid-neutralizing effect occurs within 5-15 minutes; peak effect at 30-60 minutes. |
| Duration of Action | Oral: duration of acid neutralization is 1-2 hours when taken on an empty stomach, longer (up to 3 hours) when taken after meals. Clinical note: frequent dosing may be required. |
10-20 mL (of suspension containing 200 mg aluminum hydroxide and 200 mg magnesium trisilicate per 5 mL) orally 1 hour after meals and at bedtime, up to 4 times daily.
| Dosage form | TABLET, CHEWABLE |
| Renal impairment | GFR <30 mL/min: avoid use due to risk of aluminum accumulation and neurotoxicity; GFR 30-59 mL/min: limit dose to maximum 2 doses per day and monitor serum aluminum and magnesium levels. |
| Liver impairment | No specific dosage adjustment required for hepatic impairment; use with caution in severe hepatic disease due to potential electrolyte disturbances. |
| Pediatric use | Children ≥6 years: 5-10 mL orally after meals and at bedtime; maximum 4 doses per day. Children <6 years: use not recommended. |
| Geriatric use | Initiate at lower end of adult dosing (e.g., 5-10 mL per dose) due to increased risk of electrolyte imbalance and renal impairment. Monitor for signs of aluminum or magnesium toxicity. |
| 1st trimester | Consult provider |
| 2nd trimester | Consult provider |
| 3rd trimester | Consult provider |
Clinical note
Comprehensive clinical and safety monograph for ALUMINUM HYDROXIDE AND MAGNESIUM TRISILICATE (ALUMINUM HYDROXIDE AND MAGNESIUM TRISILICATE).
| Breastfeeding | Both aluminum and magnesium compounds are poorly absorbed from the maternal gastrointestinal tract, leading to negligible excretion into breast milk. The M/P ratio is not clinically relevant due to lack of systemic absorption. These antacids are considered compatible with breastfeeding, but avoid excessive doses to prevent theoretical accumulation. |
| Teratogenic Risk | Aluminum hydroxide and magnesium trisilicate are not absorbed systemically in significant amounts, thus fetal exposure is minimal. No increased risk of congenital anomalies has been reported in epidemiologic studies. However, prolonged high-dose use in the third trimester may cause maternal and fetal hypophosphatemia or hypermagnesemia. Magnesium trisilicate may theoretically contribute to neonatal hypocalcemia or hypotonia if maternal serum magnesium levels are elevated. |
■ FDA Black Box Warning
None.
| Serious Effects |
["Hypersensitivity to any component","Renal impairment (severe) due to risk of aluminum/magnesium toxicity","Hypophosphatemia (relative)"]
| Precautions | ["Risk of aluminum toxicity in patients with renal impairment (e.g., dialysis encephalopathy, osteomalacia)","Magnesium accumulation leading to hypermagnesemia in renal failure","Hypophosphatemia with prolonged high-dose use","Constipation (aluminum) or diarrhea (magnesium) depending on formulation","Drug interactions (e.g., decreased absorption of tetracyclines, fluoroquinolones, iron, digoxin)"] |
| Food/Dietary | Avoid excessive consumption of dairy products (milk, cheese) as they may increase risk of milk-alkali syndrome; separate from iron supplements, tetracyclines, and fluoroquinolones by at least 2 hours; high-phosphate foods (e.g., soda, processed meats) may reduce antacid efficacy. |
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| Fetal Monitoring | No specific monitoring required for short-term use. With prolonged therapy (>2 weeks) or high doses, monitor maternal serum electrolytes (magnesium, phosphate, calcium) and renal function. In neonates exposed in utero, assess for signs of hypermagnesemia (hypotonia, respiratory depression) and hypophosphatemia if mother had chronic use. |
| Fertility Effects | No known effects on fertility. Aluminum and magnesium trisilicate are not absorbed systemically, thus unlikely to affect reproductive function. No human or animal data suggest impairment. |
| Clinical Pearls | Monitor for hypophosphatemia with prolonged use; avoid use in patients with renal impairment due to risk of aluminum accumulation and osteomalacia; separate from other medications by at least 2 hours to prevent chelation; use cautiously in elderly due to risk of constipation and fecal impaction. |
| Patient Advice | Take 1 hour after meals and at bedtime as directed. · Shake suspension well before use. · Do not take other medications within 2 hours of this drug. · Report prolonged constipation, black tarry stools, or abdominal pain. · Avoid use if you have kidney disease or are on dialysis. · Do not exceed recommended dosage. |