Hypermagnesemia

Definition

• Serum Mg⁺⁺ >2.3 mg/dL

Etiology:

• Insufficient excretion due to CKD
• Iatrogenic/excess intake due to overaggressive replacement, Magnesium-based laxatives/enemas use in CKD, Mg⁺⁺ administration during preeclampsia/eclampsia treatment

Clinical manifestations:

Symptoms are either cardiovascular vs neuromuscular manifestations or hypocalcemia

• Plasma Mg⁺⁺8-7.2mg/dL: Nausea, flushing, headache, lethargy, drowsiness and hyporeflexia
• Plasma Mg⁺⁺2-12mg/dL: Somnolence, hypocalcemia, areflexia, hypotension, bradycardia and ECG changes
• Plasma Mg⁺⁺ >12: Muscle paralysis leading to flaccid quadriplegia, apnea/respiratory failure, complete heart block, cardiac arrest

Evaluation:

• Order CMP, serum Mg⁺⁺ 
• Review patient history, clinical circumstances and medications

Management: 

Treatment is tailored based on severity and clinical manifestations and renal function

• Asymptomatic patients: Cessation of Mg⁺⁺ supplementation therapies
• Symptomatic patients: 1gram Calcium Gluconate IV over 10mins to antagonize Mg⁺⁺
• Moderate renal impairment (eGFR 15-45): Consider IV Isotonic fluid plus loop diuretic (e.g., Furosemide)
• Severe renal impairment (eGFR <15)/Symptomatic patients: Dialysis is the definitive therapy

Key Points:

• Clinically relevant hypermagnesemia is rare and is usually due to excessive magnesium administration in patients with CKD or impaired magnesium excretion
• Severe hypermagnesemia may need dialysis