Milk of Magnesia

Approved Indications:

• Constipation (Short-term Relief):
  Used as an osmotic laxative for occasional constipation in adults and children.
• Hyperacidity and Dyspepsia:
  Acts as an antacid to relieve symptoms such as heartburn, sour stomach, and acid indigestion.
• Peptic Ulcer Disease (PUD) [Adjunctive Use]:
  May be used for temporary relief of acid-related symptoms in patients with gastric or duodenal ulcers.
• Gastroesophageal Reflux Disease (GERD) [Mild Cases]:
  Provides short-term symptom control of reflux-related heartburn or discomfort.

Clinically Accepted Off-Label Uses:

• Bowel Preparation Before Surgery or Colonoscopy:
  Used to evacuate the bowel prior to diagnostic or surgical procedures (in combination with other agents).
• Prevention of Medication-Induced Constipation (e.g., opioid-induced):
  Occasionally used as part of a bowel regimen in patients on constipating medications.

Adults:

• For Constipation:
  30–60 mL of oral suspension (usually 400 mg/mL) once daily at bedtime or in divided doses.
  Alternatively, 2–4 tablets (500–600 mg each) once daily as needed.
• For Hyperacidity/Indigestion:
  5–15 mL orally up to four times daily as needed, preferably between meals and at bedtime.

Pediatrics:

• Children 6–11 years:
  15–30 mL of suspension (or equivalent tablets) once daily.
• Children 2–5 years:
  5–15 mL once daily. Use only under physician supervision.
• Children <2 years:
  Not recommended unless prescribed.

Elderly:

• Dose as in adults. Caution advised due to increased risk of electrolyte disturbances, especially in those with renal impairment.

Renal Impairment:

• Avoid prolonged use.
  Risk of magnesium accumulation and toxicity. Use is contraindicated in severe renal failure.

Hepatic Impairment:

• No dose adjustment necessary. Use with caution in patients with severe hepatic disease due to potential fluid or electrolyte imbalance.

Route of Administration:

• Oral (suspension, chewable tablet, or liquid formulation)

Duration of Use:

• For constipation: Do not use for more than 7 consecutive days without medical supervision.
• For antacid purposes: Short-term use as needed.

Magnesium hydroxide exerts its pharmacologic effects through two mechanisms. As an antacid, it reacts with hydrochloric acid in the stomach to form magnesium chloride and water, neutralizing gastric acid and relieving symptoms of hyperacidity. As an osmotic laxative, it draws water into the intestinal lumen by osmotic activity, increasing intraluminal fluid and stimulating peristalsis. This facilitates bowel movement and relieves constipation. Its dual role allows it to provide both gastric and intestinal symptom relief depending on the dose.

• Absorption:
  Minimal systemic absorption from the gastrointestinal tract. Small amounts of magnesium ions may be absorbed.
• Distribution:
  Absorbed magnesium is widely distributed throughout the body fluids and tissues.
• Metabolism:
  Not metabolized.
• Elimination:
  Unabsorbed magnesium is excreted in feces. Absorbed magnesium is excreted primarily by the kidneys.
• Onset of Action:
• As antacid: Within 30 minutes
• As laxative: Typically within 30 minutes to 6 hours (depending on dose)
• Duration of Action:
• Antacid effect: ~2–3 hours
• Laxative effect: ~4–6 hours

• Pregnancy:
  Generally considered safe when used occasionally and at recommended doses. Excessive use may cause electrolyte imbalance or uterine irritability. Should be avoided in the last trimester unless prescribed.
• Lactation:
  Safe for short-term use during breastfeeding. Minimal systemic absorption results in negligible excretion into breast milk, with no known harmful effects on the infant.

• Primary Class: Antacid / Osmotic Laxative
• Subclass: Non-systemic antacid and saline laxative
• Generation: Non-absorbable gastrointestinal agent

• Hypersensitivity to magnesium hydroxide or formulation excipients
• Severe renal impairment or renal failure (risk of magnesium toxicity)
• Bowel obstruction or perforation
• Severe dehydration
• Appendicitis or undiagnosed abdominal pain

• Renal Dysfunction:
  Risk of magnesium accumulation and toxicity; contraindicated in severe renal disease.
• Electrolyte Disturbances:
  Prolonged or high-dose use may cause hypermagnesemia, especially in elderly or renally impaired individuals.
• Prolonged Use:
  Chronic laxative use can result in dependency, hypokalemia, or secondary dehydration.
• Pediatric Use:
  Use in children under 6 years only with medical supervision to avoid electrolyte imbalance.
• Cardiac Arrhythmias or Neuromuscular Disorders:
  Use with caution as elevated magnesium levels can exacerbate these conditions.

Gastrointestinal:

• Diarrhea (dose-dependent)
• Abdominal cramping or discomfort
• Flatulence or bloating
• Nausea (less common)

Metabolic:

• Hypermagnesemia (especially in renal impairment):
• Symptoms: Hypotension, bradycardia, confusion, muscle weakness, respiratory depression

Others:

• Electrolyte imbalance (with prolonged use)
• Dehydration (secondary to excessive laxative action)

• Tetracyclines, Quinolones:
  May form chelates with magnesium, reducing absorption of the antibiotics → Administer at least 2–4 hours apart.
• Digoxin:
  Reduced efficacy due to decreased absorption → Space dosing appropriately.
• Iron Supplements:
  Absorption may be reduced → Avoid concurrent administration.
• Bisphosphonates (e.g., alendronate):
  Reduced absorption → Take at least 2 hours apart.

Enzyme System Involvement:

• Not significantly involved in hepatic enzyme metabolism (CYP450). Interactions are primarily physicochemical in nature.

• No recent major FDA or EMA regulatory changes.
• Clinical guidelines for constipation and acid-related disorders continue to support short-term use of magnesium hydroxide.
• Caution emphasized in updated guidelines for elderly and renally impaired populations due to the risk of hypermagnesemia.

• Temperature: Store at 20°C to 25°C (68°F to 77°F); excursions between 15°C and 30°C permitted.
• Humidity & Light: Protect from excessive moisture and direct sunlight.
• Handling Instructions:
• Shake suspension well before use.
• Store in original container with the cap tightly closed.
• Do not freeze.
• Keep out of reach of children.
• Use within the expiry date on the label.