Hypomagnesemia from malabsorption and renal magnesium wasting treated with high-dose magnesium glycinate: A case report.

BACKGROUND: Hypomagnesemia is common after Roux-en-Y gastric bypass (RYGB) due to reduced gastrointestinal absorption; however, management becomes particularly challenging when renal magnesium wasting coexists. OBJECTIVES: This report describes refractory hypomagnesemia in a post-RYGB patient with confirmed renal magnesium wasting and evaluates the role of magnesium glycinate as an alternative oral replacement strategy to oral magnesium oxide and intravenous magnesium sulfate. CASE SUMMARY: A 56-year-old female with a history of RYGB and chronic malnutrition presented with bilateral lower-extremity weakness and neuropathic symptoms. Despite high-dose intravenous magnesium sulfate administered via total parenteral nutrition and intravenous supplementation, as well as oral magnesium oxide, serum magnesium levels remained persistently low (1.1-1.9 mg/dL) with only transient correction. A markedly elevated random urine magnesium level confirmed renal magnesium wasting as a contributing factor. Oral therapy was transitioned to magnesium glycinate, a chelated formulation with alternative absorption pathways. Following this change, serum magnesium improved to 2.0-2.1 mg/dL without further need for intravenous supplementation, and episodes of severe hypomagnesemia decreased. PRACTICE IMPLICATIONS: This case highlights the importance of evaluating both gastrointestinal malabsorption and renal losses when hypomagnesemia remains refractory to standard therapy in post-bariatric surgery patients. Magnesium glycinate may represent an effective long-term oral replacement option in patients with combined malabsorption and renal magnesium wasting. Further research is needed to guide formulation selection in this population.