Hypomagnesemia and Its Association With Calcineurin Inhibitors Use in Egyptian Renal Transplant Recipients

Magnesium (Mg) is the fourth cation in the body and the second most prevalent intracellular cation. Intracellular magnesium concentrations range from 5 to 20 mmol/L; 1-5% of it is ionized, the remainder is bound to proteins.

Extracellular Mg represents only 1% of total body Mg and is mostly found in serum with concentrations ranging between 0.65 to 1.05 mmol/L and in red blood cells. It is present in three states; ionized Mg (55-70%), protein bound Mg (20-30%), and Mg complexed with anions such as bicarbonate or phosphate (5-15%). Ionized magnesium has the greatest biological activity. Magnesium homeostasis is maintained by the intestine, bones and kidneys. It is absorbed in the gut and stored in bone mineral, and excess magnesium is excreted by the kidneys and faeces. The majority of magnesium is absorbed in the small intestine by a passive paracellular mechanism, which is driven by an electrochemical gradient. A minor regulatory fraction of magnesium is transported via the transcellular transporter called transient receptor potential channel melastatin member (TRPM) 6 and TRPM7-members of the long transient receptor potential channel family.

Only about 24-76% of dietary consumed magnesium is absorbed in the gut and the rest is eliminated in the faeces.

Intestinal absorption is not directly proportional to magnesium intake but is dependent mainly on magnesium status. Hypomagnesemia is frequently observed after kidney transplantation, in part to immunosuppressive regimens including calcineurin inhibitors (CNI). The incidence of hypomagnesemia has been reported to be higher among tacrolimus compared to cyclosporine-(CsA) treated patients.

Many other factors influence Mg levels after kidney transplantation such as post-transplantation volume expansion, metabolic acidosis, insulin resistance, decreased gastro-intestinal absorption due to diarrhea, low Mg intake and medications such as diuretics or proton pump inhibitors.