When should magnesium be increased in patients?

When to Increase Magnesium Supplementation

Magnesium supplementation should be increased when serum magnesium levels fall below 0.70 mmol/L, particularly in hospitalized patients undergoing kidney replacement therapy (KRT), patients with Bartter syndrome, and those with malabsorption conditions. 1

Clinical Scenarios Requiring Magnesium Supplementation

1. Kidney Disease and Kidney Replacement Therapy

• Hypomagnesemia is common in patients undergoing continuous kidney replacement therapy (CKRT), with an incidence of 60-65% among critically ill patients 1
• Causes of magnesium depletion during KRT:
  • Diffusive or convective clearance during dialysis
  • Chelation of ionized magnesium by citrate when regional citrate anticoagulation is used
  • Loss of magnesium in the effluent as magnesium-citrate complexes 1

2. Gastrointestinal Disorders

• Supplement magnesium in patients with:
  • Diarrhea
  • Malabsorption syndromes
  • Short bowel syndrome
  • Chronic use of proton pump inhibitors 1

3. Medication-Induced Hypomagnesemia

• Increase magnesium in patients taking:
  • Diuretics (especially loop diuretics)
  • Proton pump inhibitors (chronic use)
  • Certain antibiotics 1

4. Specific Conditions

• Bartter syndrome (especially type 3): Target magnesium levels >0.6 mmol/L 1
• Refeeding syndrome
• Alcoholism
• Diabetic ketoacidosis

Diagnostic Thresholds for Intervention

• Mild hypomagnesemia: 0.64-0.76 mmol/L
• Moderate hypomagnesemia: 0.40-0.63 mmol/L
• Severe hypomagnesemia: <0.40 mmol/L 1

Treatment Approach

For Mild-Moderate Deficiency:

• Oral supplementation with organic magnesium salts (aspartate, citrate, lactate) which have higher bioavailability than magnesium oxide or hydroxide 1
• Typical dose: 12-24 mmol daily, divided into multiple doses 1

For Severe Deficiency or When Oral Route Not Feasible:

• IV magnesium sulfate: 1g (approximately 8.12 mEq) every six hours for four doses 2
• For severe hypomagnesemia: up to 250 mg/kg body weight IM within four hours 2
• Alternative IV regimen: 5g (approximately 40 mEq) added to 1L of 5% dextrose or 0.9% sodium chloride for slow infusion over three hours 2

For Patients on KRT:

• Use dialysis solutions containing magnesium rather than IV supplementation 1
• Commercial KRT solutions enriched with magnesium are preferred to prevent KRT-related hypomagnesemia 1

Special Considerations

Dosing Strategy

• Divide supplementation into multiple doses throughout the day to maintain steady levels 1
• For patients with continuous tube feeds, add supplements to the feed 1
• For oral supplementation, nighttime administration may be beneficial when intestinal transit is slowest 1

Monitoring

• Regular monitoring of serum magnesium levels is essential
• For IV supplementation in renal insufficiency, maximum dosage should not exceed 20g/48 hours with frequent monitoring of serum magnesium 2

Cautions

• Use with extreme caution in patients with renal insufficiency as magnesium is primarily excreted by the kidneys 2
• When using 1-alpha hydroxy-cholecalciferol to improve magnesium balance, monitor serum calcium to avoid hypercalcemia 1
• Avoid rapid IV administration (should not exceed 150 mg/minute) 2

Clinical Manifestations of Magnesium Deficiency to Monitor

• Neuromuscular hyperexcitability
• Cardiac arrhythmias
• Hypokalemia and hypocalcemia that are resistant to supplementation
• Seizures
• Muscle cramps and weakness

By addressing magnesium deficiency promptly and appropriately, clinicians can prevent serious complications including cardiac arrhythmias, seizures, and worsening of electrolyte imbalances that impact morbidity and mortality.