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Magnesium Preparation Gitelman — ESENeph MCQ

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ModerateElectrolyte DisordersMagnesium Preparation GitelmanESENeph

A 35-year-old man with Gitelman syndrome has persistent hypomagnesaemia (Mg2+ 0.45 mmol/L) despite oral magnesium supplementation (magnesium oxide 400 mg TDS). He has diarrhoea from the magnesium. What alternative magnesium preparation may be better tolerated?

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Correct answer: B — Magnesium glycerophosphate or magnesium aspartate – organic magnesium salts are generally better tolerated GI-wise than magnesium oxide, which has poor bioavailability and is osmotically active causing diarrhoea

Magnesium oxide has poor oral bioavailability (~4%) and the unabsorbed fraction acts as an osmotic laxative, causing diarrhoea. Organic magnesium salts (glycerophosphate, aspartate, citrate, L-threonate) have better bioavailability and GI tolerability. Slow-release preparations also improve absorption. In Gitelman syndrome, lifelong magnesium supplementation is needed due to ongoing renal wasting. Some patients require IV magnesium infusions periodically despite oral supplements. Amiloride can reduce renal magnesium loss as an adjunct.

Reference: Blanchard et al 2017 – Gitelman Management; BNF – Magnesium Preparations