Dosing and uses of Milk of Magnesia (magnesium hydroxide)
Adult dosage forms and strengths
chewable tablet
- 311mg
- 400mg
suspension
- 7.75%
- 400mg/5mL
- 800mg/5mL
- 1200mg/15mL
- 2400mg/10mL
Constipation
Magnesium hydroxide (400 mg/5 mL): 30-60 mL/day PO at bedtime or in divided doses
Magnesium hydroxide (800 mg/5 mL): 15-30 mL/day PO at bedtime or in divided doses
Chewable tablet: 8 tablets/day PO at bedtime or in divided doses
Acid Indigestion
Magnesium hydroxide (400 mg/5 mL): 5-15 mL PO q4hr; no more than 4 doses per 24-hour period
Chewable tablet: 2-4 tablets PO q4hr; no more than 4 doses per 24-hour period
Pediatric dosage forms and strengths
chewable tablet
- 311mg
- 400mg
suspension
- 7.75%
- 400mg/5mL
- 800mg/5mL
- 1200mg/15mL
- 2400mg/10mL
Constipation
<2 years: Safety and efficacy not established
Suspension
- 2-6 years: 5-15 mL/day of regular-strength liquid PO at bedtime or in divided doses
- 6-12 years: 15-30 mL/day (400 mg/5 mL) or 7.5-15 mL/day (800 mg/5 mL) PO at bedtime or in divided doses
- ≥12 years: 30-60 mL/day (400 mg/5 mL) or 15-30 mL/day (800 mg/5 mL) PO at bedtime or in divided doses
Chewable tablet
- <3 years: Not recommended
- 3-6 years: 2 tablets PO once daily or in divided doses
- 6-12 years: 4 tablets PO once daily or in divided doses
- >12 years: 8 tablets PO once daily or in divided doses
Acid Indigestion
Liquid
- <12 years: Not recommended
- ≥12 years: 5-15 mL (400 mg/5 mL) PO q4hr; no more than 4 doses per 24-hour period
Chewable tablet
- <12 years: Not recommended
- ≥12 years: 2-4 tablets PO q4hr; no more than 4 doses per 24-hour period
Milk of Magnesia (magnesium hydroxide) adverse (side) effects
Frequency not defined
Abdominal cramping
Diarrhea
Electrolyte imbalance
Hypotension
Muscle weakness
Respiratory depression
Warnings
Contraindications
Renal failure
Existing electrolyte imbalance
Appendicitis symptoms or acute surgical abdomen
Myocardial damage or heart block
Fecal impaction or rectal fissures
Intestinal obstruction or perforation
Undiagnosed abdominal pain
Cautions
Use with caution in renal insufficiency
Pregnancy and lactation
Pregnancy category: A
Lactation: Use in nursing mothers appears to be safe
Pregnancy categories
A: Generally acceptable. Controlled studies in pregnant women show no evidence of fetal risk.
B: May be acceptable. Either animal studies show no risk but human studies not available or animal studies showed minor risks and human studies done and showed no risk.
C: Use with caution if benefits outweigh risks. Animal studies show risk and human studies not available or neither animal nor human studies done.
D: Use in LIFE-THREATENING emergencies when no safer drug available. Positive evidence of human fetal risk.
X: Do not use in pregnancy. Risks involved outweigh potential benefits. Safer alternatives exist.
NA: Information not available.
Pharmacology of Milk of Magnesia (magnesium hydroxide)
Mechanism of action
Laxative: Promotes osmotic retention of fluid, which distends the colon with increased peristaltic activity and stimulates bowel evacuation
Antacid: Reacts with hydrochloric acid in stomach to form magnesium chloride
Absorption
Bioavailability: 15-30%
Onset: 0.5-6 hr (laxative)
Elimination
Excretion: Urine (up to 30% as absorbed magnesium), feces (as unabsorbed drug)
