Magnesium Oxide

Approved Indications:

• Hypomagnesemia: Treatment and prevention of low serum magnesium levels due to chronic illness, diuretic therapy, or gastrointestinal losses.
• Antacid Use: Relief of heartburn, sour stomach, indigestion, and gastric hyperacidity.
• Occasional Constipation: Used as a mild osmotic laxative for short-term relief.
• Magnesium Supplementation: Maintenance of adequate magnesium levels in individuals with increased requirements (e.g., in diabetes, alcoholism, or prolonged diuretic therapy).

Clinically Accepted Off-Label Uses:

• Migraine Prophylaxis: Used in patients with recurrent migraines associated with magnesium deficiency.
• Nocturnal Leg Cramps: Occasionally prescribed in magnesium-deficient patients to relieve nighttime leg cramps.
• Supportive Use in Preeclampsia: Used as a preventive supplement in pregnancy for magnesium maintenance (not a substitute for magnesium sulfate in treatment).

Route: Oral (tablets, capsules, or powder)

Adults:

• Magnesium Deficiency: 250–500 mg orally 2 to 4 times daily, adjusted based on clinical need.
• Antacid: 400–800 mg orally, up to 4 times daily after meals and at bedtime.
• Constipation: 400–1,000 mg once daily at bedtime with a full glass of water.
• Supplementation: 250–500 mg once or twice daily.

Pediatric Patients:

• Supplementation:
• Ages 1–3 years: 40–80 mg/day
• Ages 4–8 years: 110–200 mg/day
• Ages ≥9 years: Adult dosage may apply

Dosing should be individualized and supervised by a physician.

Geriatric Use:

• Same as adult dosing; however, initiate at lower end of dose range due to reduced renal function.

Special Populations:

• Renal Impairment: Use is contraindicated or requires extreme caution due to the risk of magnesium accumulation.
• Hepatic Impairment: No dose adjustment generally required.

Administration Instructions:

• Take with meals to minimize gastric discomfort.
• Swallow tablets whole with water.
• Avoid co-administration with tetracyclines or fluoroquinolones; separate doses by 2 to 4 hours.

Magnesium oxide acts as an antacid and magnesium supplement. When ingested, it reacts with hydrochloric acid in the stomach to form magnesium chloride and water, thereby neutralizing gastric acidity and relieving dyspeptic symptoms. Magnesium ions also have an osmotic effect in the intestine, drawing water into the bowel and promoting peristalsis, which results in laxative action. Furthermore, absorbed magnesium is vital for many enzymatic functions involved in energy metabolism, neuromuscular activity, and protein synthesis.

• Absorption: Poorly absorbed in the gastrointestinal tract (approximately 15–50%), depending on dose and magnesium status.
• Onset of Action:
• Antacid effect: within 30 minutes
• Laxative effect: within 3–6 hours
• Bioavailability: Low due to limited solubility and absorption.
• Distribution: Distributed widely, especially in bone and intracellular fluid.
• Metabolism: Not metabolized.
• Elimination:
• Absorbed magnesium is eliminated by the kidneys.
• Unabsorbed magnesium is excreted in the feces.

• Pregnancy: Considered safe for short-term use. Magnesium oxide is generally recognized as safe during pregnancy when used within the recommended dietary allowance (RDA). High-dose or prolonged use should be avoided unless directed by a physician.
• Lactation: Excreted in small amounts into breast milk but is not expected to cause adverse effects in nursing infants. Safe during breastfeeding at normal doses.
• Caution: Prolonged or high-dose use in pregnancy or lactation should only be done under medical supervision.

• Primary Class: Mineral and Electrolyte Supplement
• Secondary Class: Antacid and Osmotic Laxative

• Known hypersensitivity to magnesium oxide or any formulation component
• Severe renal impairment or renal failure
• Myocardial damage in the presence of hypermagnesemia
• Heart block
• Intestinal obstruction or ileus (if used as a laxative)

• Renal Dysfunction: May lead to serious hypermagnesemia; avoid or use cautiously with close monitoring.
• Prolonged Use: Long-term use may result in electrolyte imbalance or dependency (as a laxative).
• Cardiac Disorders: Use with caution in patients with bradycardia or heart block.
• Elderly Patients: Increased sensitivity due to declining renal function; monitor serum magnesium and renal parameters.
• Toxicity Symptoms: Include nausea, flushing, hypotension, respiratory depression, and muscle weakness.

Common (Mild to Moderate):

• Gastrointestinal: Diarrhea, abdominal cramps, nausea, bloating
• Other: Bad taste, belching

Serious or Rare:

• Electrolyte Disorders: Hypermagnesemia (especially in renal dysfunction)
• Neurologic: Confusion, drowsiness, muscle weakness
• Cardiovascular: Bradycardia, hypotension, arrhythmias
• Respiratory: Respiratory depression (in toxicity)

Onset is typically dose-dependent; toxicity occurs with high or prolonged doses.

• Tetracyclines & Fluoroquinolones: Reduced absorption due to chelation. Separate dosing by 2–4 hours.
• Bisphosphonates: Decreased absorption. Separate by several hours.
• Levothyroxine: Reduced bioavailability. Administer 4 hours apart.
• Digoxin: Hypermagnesemia may interfere with cardiac conduction.
• Calcium Channel Blockers: Additive effects on bradycardia and hypotension.
• Alcohol: Can worsen gastrointestinal irritation and electrolyte loss.
• Metabolic Enzymes: Not a CYP450 substrate; no direct hepatic enzyme involvement.

• No recent FDA or EMA labeling changes for magnesium oxide.
• Guidelines continue to recommend careful use in individuals with renal impairment.
• Continued emphasis on short-term use only for constipation and dyspepsia.
• Magnesium supplementation guidelines updated by the National Institutes of Health (NIH) reinforce the importance of avoiding excessive dosing.

• Temperature: Store at 20°C to 25°C (68°F to 77°F); excursions permitted between 15°C and 30°C.
• Humidity: Protect from moisture; store in a dry environment.
• Light: Keep in a well-closed container, protected from light.
• Handling Instructions: Avoid exposing tablets to humidity; close bottle tightly after each use.
• Reconstitution: Not applicable for tablets or capsules. Powder forms should be reconstituted with clean water immediately before use.