A case of refractory hypomagnesemia: when supplementation is not enough

Abstract

A 90-year-old male patient was hospitalized following syncope without prodromal symptoms. Clinical examination revealed a positive Chvostek sign and brisk deep tendon reflexes. Laboratory tests demonstrated severe hypomagnesemia (0.21 mmol/L), hypokalemia (2.8 mmol/L), and hypocalcemia (corrected calcium 1.81 mmol/L), along with a prolonged QTc interval (510 msec) on electrocardiography. Initial management included intravenous electrolytes replacement, discontinuation of pantoprazole (known to impair magnesium absorption) and metformin (associated with chelation effects). After an initial improvement, we switched from intravenous to oral magnesium supplementation, but magnesium levels declined again. Further history-taking revealed that the patient consumed exclusively soda (carbonated soft drinks such as cola-based beverages). These drinks contain phosphoric acid, which acts as a chelating agent, binding magnesium and inhibiting its intestinal absorption. Discontinuation of this beverage intake led to normalization of magnesium levels. Finally, the syncope of our patient is most likely attributable to an arrhythmia secondary to electrolyte disturbances. The most severely altered electrolyte is magnesium, which has contributed to the development of both hypokalemia and hypocalcemia. The origin of this disturbance is probably multifactorial, involving the use of proton pump inhibitors (and possibly metformin), the malnutrition commonly seen in elderly patients, and the exclusive consumption of soda, resulting in a chelating effect.