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
- Monitor DTRs, rebound hypermagnesemia will have hyporeflexia