Hypermagnesemia

Almost always the result of advanced stages of chronic kidney disease (CKD) and impaired magnesium excretion

Antacids and laxatives are underrecognized sources of magnesium

Pregnant patients may have severe hypermagnesemia from intravenous magnesium therapy for preeclampsia and eclampsia

Magnesium replacement should be done cautiously in patients with CKD, and dose reductions up to 75% may be necessary to avoid hypermagnesemia

Muscle weakness

Decreased deep tendon reflexes

Mental obtundation

Confusion

Weakness, even flaccid paralysis

Ileus, urinary retention, hypotension

In severe cases, respiratory muscle paralysis or cardiac arrest

Serum magnesium is elevated

In the common setting of CKD, elevated blood urea nitrogen, serum creatinine, phosphate, and uric acid; serum K⁺ may be elevated

Serum Ca²⁺ is often low

ECG may show increased PR interval, broadened QRS complexes, and peaked T waves, probably related to associated hyperkalemia

Exogenous sources of magnesium should be discontinued

Calcium antagonizes Mg²⁺ and may be given intravenously as calcium chloride, 500 mg or more at a rate of 100 mg (4.1 mmol)/min

Hemodialysis or peritoneal dialysis may be necessary

Long-term use of magnesium hydroxide and magnesium sulfate should be avoided in patients with advanced stages of CKD