magnesium hydroxide
Concentrated Phillips’ Milk of Magnesia, Milk of Magnesia, Phillips’ Milk of Magnesia

Available forms
Available without a prescription
Liquid: 400 mg/5 ml, 800 mg/5 ml
Suspension: 77.5 mg/g
Suspension (concentrated): 10 ml (equivalent to 30 ml of milk of magnesia)
Tablets: 300 mg, 600 mg
Tablets (chewable): 311 mg

Indications and dosages
 Constipation, bowel evacuation before surgery. Adults and children older than age 6: 10 to 20 ml (2 to 4 teaspoons) Concentrated Milk of Magnesia P.O.; 15 to 60 ml (1 to 4 tablespoons) Milk of Magnesia P.O.
 As a laxative. Adults and children age 12 and older: 30 to 60 ml (2 to 4 tablespoons) h.s. or upon arising, followed by about 240 ml (8 oz) of liquid.
Children ages 6 to 11: Don’t use dosage cup. 15 to 30 ml (1 to 2 tablespoons) followed by about 240 ml (8 oz) of liquid.
Children ages 2 to 5: Don’t use dosage cup. 5 to 15 ml (1 to 3 teaspoons) followed by about 240 ml (8 oz) of liquid.
 As an antacid. Adults and children age 12 and older: Don’t use dosage cup. 5 to 15 ml (1 to 3 teaspoons) with a little water, up to q.i.d.

Pharmacodynamics
Antiulcer action: Magnesium hydroxide neutralizes gastric acid, decreasing the direct acid irritant effect. This increases pH, which, in turn, leads to pepsin inactivation. Drug also enhances mucosal barrier integrity and improves gastric and esophageal sphincter tone.
Antacid action: Drug reacts rapidly with hydrochloric acid in the stomach to form magnesium chloride and water.
Laxative action: Magnesium hydroxide produces its laxative effect by increasing the osmotic gradient in the gut and drawing in water, causing distention that stimulates peristalsis and bowel evacuation.

Pharmacokinetics
Absorption: About 15% to 30% may be absorbed systemically (posing a potential risk to patients with renal failure).
Distribution: None.
Metabolism: None.
Excretion: Unabsorbed drug is excreted in feces; absorbed drug is excreted rapidly in urine.

Contraindications and precautions
Contraindicated in patients with abdominal pain, nausea, vomiting, or other symptoms of appendicitis or acute surgical abdomen and in those with myocardial damage, heart block, fecal impaction, rectal fissures, intestinal obstruction or perforation, or renal disease. Also contraindicated in women about to deliver.
  Use cautiously in patients with rectal bleeding.

Interactions
Drug-drug. Chlordiazepoxide, chlorpromazine, dicumarol, digoxin, iron salts, isoniazid: Using magnesium hydroxide with aluminum hydroxide may decrease absorption rate of these drugs. Separate administration times.
Enteric-coated tablets: Causes premature release of these drugs. Separate administration times.
Quinolones, tetracyclines: Decreases absorption of these drugs. Separate administration times.

Adverse reactions
GI: abdominal cramping, nausea, diarrhea, laxative dependence (with long-term or excessive use).
Metabolic: fluid and electrolyte disturbances (with daily use).

Effects on lab test results
• May increase magnesium level.

Overdose and treatment
No information available.

Special considerations
• Give drug at least 1 hour apart from enteric-coated drugs; shake suspension well.
• After giving drug through nasogastric tube, flush tube with water to clear it.
• Monitor patient for signs and symptoms of hypermagnesemia, especially if patient has impaired renal function.
Breast-feeding patients
• Some magnesium may appear in breast milk, but no problems have been linked to use by breast-feeding women.
Pediatric patients
• Use as an antacid in children younger than age 6 requires a well-established diagnosis because children tend to give vague descriptions of symptoms.

Patient education
• Caution patient to avoid overuse to prevent laxative dependence.
• Instruct patient to shake suspension well or to chew tablets well.
• Encourage patient using drug as a laxative to maintain adequate fluid intake, diet, and exercise.

Reactions may be common, uncommon, life-threatening, or COMMON AND LIFE THREATENING.
◆ Canada only
◇ Unlabeled clinical use