Fluids, Electrolytes & Nutrition: Magnesium (Mg)

Hypermagnesemia

Causes

  • Overdose in Renal Failure Patients on Laxatives or Antacids (PPI)
  • Massive Oral Ingestion
  • Magnesium Enemas

Presentation

  • Lethargy
  • Nausea
  • Headache
  • Diminished Deep Tendon Reflexes (DTR)
  • Bradycardia
  • Muscle Paralysis or Respiratory Failure if Severely High (> 10 mg/dL)

Treatment

  • Primary Treatment: Normal Saline & Furosemide
    • May Require Dialysis
  • First Step: Give IV Calcium (Antagonize Cardiovascular/Neuromuscular Effects)
  • Patients with Normal Renal Function Generally Require No Treatment, Just Cessation of Magnesium Therapy

Hypomagnesemia

Causes

  • Massive Diuresis
  • Chronic TPN without Magnesium Replacement
  • Alcohol Abuse
  • Uncontrolled Diabetes
  • Chronic PPI Therapy

Presentation

  • Tetany & Seizures (Similar to Hypocalcemia)
  • Weakness
  • Coma
  • Other Electrolyte Deficiencies:
    • Hypokalemia
      • From Renal Potassium Wasting – Potassium (ROMK) Channels Secrete Potassium (Normally Inhibited by Magnesium)
      • Relatively Refractory to Potassium Supplementation Until Magnesium is Corrected
    • Hypocalcemia
      • Blocks PTH Release (Hypoparathyroidism)
      • End-Organ PTH-Resistance
      • Vitamin D Deficiency
  • EKG Changes:
    • Widened QRS
    • Prolonged QT Interval
    • Prolonged PR Interval
    • Polymorphic Ventricular Tachycardia

Treatment