What are the medical uses for magnesium oxide (mag ox)?

Medical Uses for Magnesium Oxide (Mag Ox)

Magnesium oxide is primarily used as an antacid, laxative for constipation, and for treating hypomagnesemia, with specific dosing recommendations depending on the indication. 1, 2

Primary Clinical Applications

1. Treatment of Constipation

• Conditionally recommended by the American Gastroenterological Association for chronic idiopathic constipation 2
• Typical dosing for constipation ranges from 500-1000 mg daily 3
• Works as an osmotic laxative by drawing water into the intestines, making stool softer and easier to pass 4
• Should be started at a lower dose and increased if necessary 2
• Avoid use in patients with renal insufficiency due to risk of hypermagnesemia 2, 5

2. Management of Hypomagnesemia

• Commonly given as 12-24 mmol daily (approximately 480-960 mg) 2
• Best administered at night when intestinal transit is slowest to improve absorption 2
• May be used when oral magnesium supplements do not normalize magnesium levels 2
• Contains more elemental magnesium than other magnesium salts but has lower bioavailability 6

3. Antacid Properties

• FDA-approved as an antacid with 400mg tablets containing 241.2mg of elemental magnesium 1
• Neutralizes stomach acid by increasing gastric pH 7

Special Considerations and Precautions

Risk Factors for Hypermagnesemia

• Estimated glomerular filtration rate ≤ 55.4 mL/min 5
• Blood urea nitrogen ≥22.4 mg/dL 5
• MgO dose ≥1650 mg/day 5
• Duration of MgO administration ≥36 days 5

Drug Interactions

• Reduced efficacy when combined with gastric acid secretion inhibitors (H2 receptor antagonists or proton pump inhibitors) due to decreased conversion to MgCl2 in less acidic environment 7
• Higher dosing levels may be required in patients taking H2RA or PPI 7

Administration Pearls

• For hypomagnesemia, magnesium oxide is usually given at night when intestinal transit is assumed to be slowest 2
• For constipation, starting at a lower dose and increasing as needed is recommended 2
• Approximately 90% of MgO tablets dissolve within 120 minutes after ingestion 8
• About 15% of orally administered magnesium is absorbed into the bloodstream, while 85% is excreted in feces 8

Algorithm for Use in Clinical Practice

1. For constipation management:

   • Start with dietary modifications and increased fiber intake
   • Add magnesium oxide at 500 mg daily if insufficient response
   • May increase to 1000 mg daily if needed 2, 4
   • Consider adding a stimulant laxative or switching to PEG if constipation remains unresolved 4

2. For hypomagnesemia management:

   • Begin with 12 mmol magnesium oxide at night 2
   • May increase to 24 mmol daily if needed 2
   • If oral supplements fail to normalize levels, consider oral 1-alpha hydroxy-cholecalciferol in gradually increasing doses 2
   • Monitor serum calcium to avoid hypercalcemia when using vitamin D supplements 2

3. For antacid purposes:

   • Standard dose is 400 mg (241.2 mg elemental magnesium) 1

Contraindications

• Significant renal impairment (creatinine clearance <20 mL/min) due to risk of hypermagnesemia 2, 3, 5
• Use with caution in elderly patients due to increased risk of electrolyte disturbances 4