Hypomagnesemia

Hypomagnesemia

• Magnesium <0.7-1.3/1.6
  • PTH release is impaired <1mg/dl
• Causes
  • Most commonly caused by chronic combo of (impaired intestinal absorption and increased renal excretion):
    • Impaired absorption
      • Malabsorption, Diarrhea, Pancreatitis
      • Omeprazole, Foscarnet
      • Alcoholism, NG suction
    • Increased Excretion
      • Loop and Thiazide diuretics
      • SIADH
    • Medications
      • Aminoglycosides, Amphotericin B, Cisplatin, Cyclosporine, Pentamidine, PPIs
    • Other
      • Prolonged fasting, fistulas, TPN, diuretics, Bartter Syndrome, frugs, renal transplant, post-Parathyroidectomy, DKA, lactation, burns, pancreatitis
      • Aminoglycosides, AMP B, Cisplatin, Cyclosporine, Pentamidine, PPIs
      • Hypoparathyroidism (normal or low serum phosphate)
• Symptoms
  • Lethargy, confusion, tremor, ataxia, nystagmus, tetany, seizures
  • Atrial and Ventricular arrhythmias
    • Especially if on digoxin
  • Neuromuscular irritability and tetany with weakness
  • Delirium and coma
  • EKGs
    • PR and QT prolongation
    • Widened QRS
    • T wave flattening
    • Torsade de pointes if severe
• Labs
  • Refractory Hypocalcemia
  • Refractory Hypokalemia
    • Renal potassium wasting
      • Excess potassium efflux from renal tubular cells
• Testing
  • Urine Mg >2/24hrs or FEMg >2%: Increased Renal Excretion
• Treatment
  • Max rate 2g Mg Sulfate/hr, recommended 1g Mg Sulfate/hr
    • 10% solution over 10minutes followed by 1g in 100ml/hr
  • Oral unless symptomatic
  • Serum 1.9-2: IV 1g Mg Sulfate, recheck in AM
  • Serum 1.7-1.9: IV 2g Mg Sulfate, recheck in AM
  • Serum 1.6-1.7: IV 3g Mg Sulfate, recheck in 4-6hrs if symptomatic, otherwise AM
  • Serum <1.5:
  • Monitor DTRs, rebound hypermagnesemia will have hyporeflexia