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Hypermagnesemia is an electrolyte disorder in which serum magnesium levels are above the reference range. The most common cause is renal insufficiency in combination with increased magnesium intake (e.g., from laxatives). Other causes include magnesium therapy, hypothyroidism, and rhabdomyolysis. Mild hypermagnesemia is often asymptomatic but higher magnesium levels (e.g., above 4–5 mg/dL) can cause neuromuscular, gastrointestinal, and cardiovascular symptoms, including ECG abnormalities. In very severe cases, hypermagnesemia can lead to cardiac arrest and death. Concomitant electrolyte imbalances (e.g., hypocalcemia) should be assessed, as they may worsen symptoms. The most important treatment step is the discontinuation of magnesium intake, which is sufficient for most asymptomatic or stable patients. Symptomatic patients may be treated with IV isotonic fluids, IV calcium, and loop diuretics. Acute dialysis should be considered in severe cases.
Hypermagnesemia is a serum magnesium concentration above 2.2–2.4 mg/dL (0.91–1.0 mmol/L). 
- Decreased magnesium elimination 
- Increased magnesium intake 
- Increased tissue breakdown 
Mild hypermagnesemia is often asymptomatic; symptoms typically occur if magnesium levels are above 4–5 mg/dL. 
Because most of the total magnesium in the body is located intracellularly, serum magnesium levels may not accurately reflect total body magnesium levels, and symptoms may not correlate with specific serum levels. 
Laboratory studies 
- Serum electrolytes
- Renal function tests: often show findings of renal impairment, e.g., ↑ creatinine, ↓ estimated GFR
- Coagulation studies: may show decreased clotting time
- Further studies: Consider depending on the suspected cause of hypermagnesemia (e.g., ).
Stable and asymptomatic patients with normal renal function usually do not require medical therapy.
All patients 
- Discontinue magnesium-containing medication and any other magnesium intake.
- Identify and treat the underlying , e.g.:
Significant and/or symptomatic hypermagnesemia 
- Supportive treatment
Life-threatening hypermagnesemia (e.g., patients with hypotension or respiratory failure)
- Consider calcium administration as a temporizing measure until acute dialysis can be arranged.
- Agents: Follow local protocols for dosing where possible.
- For patients in cardiac arrest, follow ACLS algorithm and management in “Reversible causes of cardiac arrest.”
- Mildly symptomatic patients: (with normal renal function): Consider loop diuretics, e.g., furosemide. (off-label) 
- If magnesium intake was oral: Consider magnesium-free laxatives or enemas.