Case Presentation: Hypermagnesemia is a rare, but potentially fatal clinical condition. We report a case of symptomatic hypermagnesemia in an 84-year-old female with stage 4 CKD who was taking daily magnesium oxide with intermittent milk of magnesia for chronic constipation. She presented with confusion, delayed verbal and motor response, and dyspnea and her presentation was initially thought to be an acute exacerbation of heart failure. The following day, a serum magnesium level was checked and noted to be elevated at 5.7 mg/dl. Her creatinine was also elevated at 3.98 (baseline 2.2). An EKG showed a paced rhythm with prolonged PR and QT intervals. She was diagnosed with magnesium toxicity and emergent hemodialysis was recommended. However, as she was receiving plavix and heparin, there was concern she would be a bleeding risk with emergent trialysis line placement. She was treated with IV fluids, calcium gluconate, and loop diuretics with a plan to initiate dialysis the following day. Given the dramatic neurologic improvement with IV calcium, dialysis was held, and she continued medical management including the addition of metolazone. Her course was complicated by ileus, and she was treated with an aggressive bowel regimen. Despite improvement, her magnesium levels plateaued at 4.3 mg/dl and her creatinine remained elevated. She was initiated on hemodialysis for ESKD, which resulted in normalization of magnesium levels.
Discussion: Hypermagnesemia is rare and around 86% of cases are missed. Magnesium homeostasis is maintained through absorption in the small intestine and colon and renal excretion. Up to 70% of filtered magnesium is excreted by the kidneys, thus hypermagnesemia is seen in patients with severe renal dysfunction. However, colonic hypomobility can predispose to increased magnesium absorption through longer transit times. This is exacerbated by increased ingestion of magnesium containing laxatives in patients with chronic constipation. Hypermagnesemia can also promote ileus. In these cases, discontinuing the laxative and initiating alternative therapies to clear the bowels is imperative to halt further magnesium absorption. Although large volumes of IV fluids are recommended in the treatment of hypermagnesemia, our case took place during a nationwide IV fluid shortage. As a result, our patient was treated with 750 mL IV fluid and 2L of oral water daily. Furthermore, IV calcium gluconate is a mainstay in the treatment of hypermagnesemia as it reverses cardiac toxicity and neurotoxicity. In addition, IV loop diuretics are widely used to promote renal magnesium excretion through its action on the thick ascending loop of Henle. Furthermore, thiazide diuretics, such as metolazone, may provide a synergistic effect on magnesium excretion by acting at the distal convoluted tubule. However, our patient had minimal improvement with this therapy, likely due to her severe CKD.
Conclusions: Magnesium containing laxatives should be used with caution in elderly patients, especially those with renal dysfunction and colonic hypomobility. Prompt discontinuation of the magnesium supplement along with clearance of the bowels is imperative to prevent further magnesium absorption. Furthermore, diuretics may have a limited role in treating patients with ESKD, who may ultimately need hemodialysis. As symptoms of hypermagnesemia may be nonspecific, we should maintain a high clinical suspicion particularly in these at-risk groups.