Disorders of Magnesium: Hypermagnesemia

Abstract

Hypermagnesemia, which is defined as serum [Mg²⁺] > 2.7 mg/dL, is not a common electrolyte disorder in individuals with normal renal function. As stated in Chap. 23, the kidney is able to maintain serum [Mg²⁺] within normal range by enhancing its excretion in situations of excess Mg²⁺ intake. Therefore, a decrease in glomerular filtration rate (GFR), as seen in chronic kidney disease, seems to be the most common cause of hypermagnesemia. The other major cause is an exogenous load of Mg²⁺. Excess intake of Mg²⁺ can occur when a patient with preeclampsia (a condition characterized by proteinuria and hypertension during third trimester of pregnancy) is treated with magnesium sulfate or when individuals take Mg²⁺-containing antacids or enemas. Infants born to mothers who were treated with magnesium for preeclampsia/eclampsia may develop hypermagnesemia. Elderly individuals are particularly susceptible to Mg²⁺ toxicity because of decreased renal function with aging and excessive use of Mg²⁺-containing medications and vitamins. Subjects with familial hypocalciuric hypercalcemia may have elevated Mg²⁺ levels. Acromegalics and patients with adrenal insufficiency may have hypermagnesemia. The various causes of hypermagnesemia are summarized in Table 25.1.