What is the recommended dosing for magnesium oxide in inpatient (hospital) settings?

Magnesium Oxide Inpatient Dosing

For inpatient settings, magnesium oxide should be dosed at 12-24 mmol (480-960 mg) daily, typically administered at night when intestinal transit is slowest to maximize absorption. 1

Indications for Magnesium Oxide in Inpatient Settings

• Hypomagnesemia: Primary indication for magnesium supplementation
• Constipation: Used as an osmotic laxative
• Electrolyte replacement: For patients with GI losses or poor intake

Dosing Recommendations

For Hypomagnesemia:

• Initial dose: 12 mmol (480 mg) magnesium oxide daily 1
• Maintenance dose: Can be increased to 24 mmol (960 mg) daily if needed 1, 2
• Administration timing: Preferably at night when intestinal transit is slowest 1
• Formulation: Often given as gelatine capsules containing 4 mmol (160 mg) magnesium oxide each 1

For Polymorphic Ventricular Tachycardia (Torsades de Pointes):

• Acute treatment: 1-2 g IV magnesium sulfate (not oxide) over 15 minutes 1
• Monitoring: Follow magnesium levels if frequent or prolonged dosing required, particularly in patients with impaired renal function 1

Special Considerations

Patients with Jejunostomy/Short Bowel:

• Oral magnesium oxide may be insufficient; IV supplementation often required 1
• Rehydration to correct secondary hyperaldosteronism is crucial before magnesium replacement 1

Patients on Acid Suppressants:

• Higher doses of magnesium oxide may be required in patients taking H2-receptor antagonists or proton pump inhibitors 3
• The laxative effect of MgO is decreased due to lower solubility at higher gastric pH 3

Renal Impairment:

• Contraindication: Avoid in patients with significant renal insufficiency due to risk of hypermagnesemia 1, 2
• Monitoring: Regular assessment of serum magnesium levels is essential 2

Monitoring Parameters

1. Serum magnesium levels: Target range 1.8-3.0 mmol/L 4
2. Signs of toxicity:
   • Loss of patellar reflex (at 3.5-5 mmol/L) 4
   • Respiratory depression (at 5-6.5 mmol/L) 4
   • Cardiac conduction abnormalities (>7.5 mmol/L) 4
3. Renal function: Especially important in patients receiving prolonged therapy 2

Clinical Pearls

• Magnesium oxide requires conversion to magnesium chloride in the stomach to be effective 3
• Response to oral magnesium supplementation may be poor in patients with gastric acid suppression 3
• For severe hypomagnesemia or when rapid correction is needed, IV magnesium sulfate is preferred over oral magnesium oxide 2, 5
• For patients requiring maintenance of serum magnesium >2.0 mg/dL, IV magnesium sulfate 2g may need to be administered at least twice daily 5

Potential Side Effects

• Diarrhea (most common)
• Abdominal cramping
• Nausea
• Hypotension (with rapid IV administration)
• Hypermagnesemia (in renal impairment)

Magnesium oxide is generally well-tolerated when appropriately dosed and monitored, making it a suitable option for inpatient magnesium supplementation in patients with normal renal function.