IV Mg supplementation

 Q: Up to what percentage of administrated intravenous (IV) magnesium (Mg) is lost in urine? 

 Answer: 50% 

 IV supplementation of Mg is not a very efficacious route of replacement, though in ICU oral route is not feasible many times. The kidney is the major site of active magnesium transport in the human body. Whenever IV mg is infused it causes a transient elevation of plasma magnesium concentration. This leads to negative feedback and decreases reabsorption of Mg in the kidney's loop of Henle. Up to 50 percent of the administrated IV Mg gets excreted in the urine. Moreover, cells do not absorb Mg quickly. The serum Mg level does not adequately reflect the intracellular level. 

Oral supplementation is efficacious but in hospitalized patients, either this route may not be available or contributes to diarrhea.

#electrolytes

References:

1. Seo JW, Park TJ. Magnesium metabolism. Electrolyte Blood Press. 2008;6(2):86-95. doi:10.5049/EBP.2008.6.2.86 

2. Judith Blaine, Michel Chonchol and Moshe Levi Renal Control of Calcium, Phosphate, and Magnesium Homeostasis CJASN July 2015, 10 (7) 1257-1272; DOI: https://doi.org/10.2215/CJN.09750913