INTRODUCTION

Hypermagnesemia is an uncommon problem in the absence of magnesium administration or kidney failure. When it occurs, the elevation in the plasma magnesium concentration is usually mild (<3 mEq/L, 3.6 mg/dL, or 1.5 mmol/L) and the patient is asymptomatic. However, clinical symptoms may be seen when the plasma magnesium concentration exceeds 4 mEq/L (4.8 mg/dL or 2 mmol/L).

The causes, symptoms, and treatment of hypermagnesemia are reviewed in this topic. The normal regulation of magnesium balance and the different units used to measure the plasma magnesium concentration are discussed separately. (See "Regulation of magnesium balance".)

CAUSES OF HYPERMAGNESEMIA

Kidney impairment — Hypermagnesemia can be seen in 10 to 15 percent of hospitalized patients, usually in the setting of kidney failure. Plasma magnesium levels rise as kidney function declines since there is no magnesium regulatory system other than urinary excretion [5]. The typical patient with end-stage kidney disease (ESKD), for example, has a plasma magnesium concentration of 2 to 3 mEq/L (2.4 to 3.6 mg/dL or 1 to 1.5 mmol/L). In patients on dialysis, the plasma magnesium concentration is primarily determined by magnesium intake. This was shown in a cross-sectional study of patients on hemodialysis who completed a dietary questionnaire; the correlation between estimated dietary magnesium intake and the serum magnesium was 0.87 [6]. In addition, hypermagnesemia (defined as a serum magnesium greater than 1.5 mmol/L) occurred with magnesium intakes as low as 281 mg/day, which is considerably lower than the average intake in the general population. Severe and symptomatic hypermagnesemia can also be induced when exogenous magnesium is given as antacids or laxatives in usual therapeutic doses [7]. As a result, these drugs are contraindicated in patients with renal impairment.