Epidemiology & Risk Factors

Renal Insufficiency: Most common predisposing factor (GFR < 30 mL/min).
Exogenous Intake:
- iatrogenic: IV MgSO4 infusion for preeclampsia/eclampsia or neuroprotection in preterm labor.
- Laxatives (e.g., milk of magnesia) or antacids containing Mg (especially in elderly with CKD).
Other Causes: Tumor lysis syndrome, rhabdomyolysis, adrenal insufficiency (addisonian crisis), diabetic ketoacidosis (DKA).
Pathophysiology: Mg acts as a natural Ca-channel blocker

Clinical Features

Mild (Mg 2.5–5.0 mEq/L):
- Nausea, vomiting, flushing, headache.
- Hyporeflexia (diminished deep tendon reflexes - DTRs).
Moderate (Mg 5.0–10.0 mEq/L):
- Loss of DTRs (earliest sign of toxicity in preeclampsia).
- Somnolence, muscle weakness, hypotension, bradycardia.
- ECG changes: Prolonged PR interval, widened QRS, prolonged QT interval.
Severe (Mg > 10.0 mEq/L):
- Respiratory depression/paralysis (due to neuromuscular blockade).
- Complete heart block, cardiac arrest.

Initial: Serum Mg level > 2.2 mEq/L (hypermagnesemia typically becomes symptomatic at > 4.0 mEq/L).
Key Labs:
- BMP (BUN/Cr for renal function, concomitant hypocalcemia, hyperkalemia).
- Ionized Calcium (hypocalcemia often coexists due to Mg-induced suppression of PTH secretion).
Diagnostic Workup:
- ECG: Look for bradycardia, AV blocks, QRS widening, or peaked T waves.

Hypercalcemia: Diff by hyperreflexia (in early stages), shortened QT interval (vs prolonged QT/PR in hypermagnesemia), and high serum Ca.
Hypokalemia/Hyperkalemia: Diff by unique ECG patterns (U-waves/flat T-waves in hypokalemia; peaked T-waves/sine wave in hyperkalemia) and direct serum K measurement.
Lambert-Eaton Myasthenic Syndrome / Myasthenia Gravis: Diff by subacute/chronic progression, lack of sensory or autonomic cardiac changes, and normal serum Mg.
Guillain-Barré Syndrome: Diff by ascending paralysis, albuminocytologic dissociation on LP, and normal electrolytes.

Stop Exogenous Mg: Discontinue all Mg-containing infusions, antacids, or laxatives immediately.
Cardioprotection (If Symptomatic/Severe):
- IV Calcium Gluconate (or Calcium Chloride) 1 g IV over 2–5 mins to antagonize neuromuscular and cardiac effects of Mg.
Enhance Elimination:
- Normal saline (0.9% NaCl) + Loop diuretics (Furosemide): If renal function is preserved, to promote renal Mg excretion.
Refractory/Renal Failure:
- Hemodialysis: Indicated for severe hypermagnesemia (Mg > 8.0 mEq/L with symptoms) in patients with end-stage renal disease (ESRD) or severe CKD.

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