Magnesium

The source of magnesium is dietary and most is intracellular (see Table 6.1). Extracellular magnesium is present in 3 forms: free (55%) which is thought to be the biologically active form, protein bound (20-30%), and complexed (15-25%). Unlike calcium which is 40% protein bound, magnesium is only 20-30% protein bound and therefore less affected by hypoalbuminemia than calcium. Magnesium is absorbed primarily in the ileum and the kidneys regulate magnesium balance.

Hypermagnesemia

Since magnesium is predominantly excreted by the kidneys, hypermagnesemia may be seen in animals with renal disease or postrenal obstruction. The administration of Mg⁺-containing products can result in iatrogenic hypermagnesemia.

Hypomagnesemia

Hypomagnesemia is generally due to dietary deficiency or decreased intake. In hospitalized ill patients, hypomagnesemia may be due to a lack of dietary intake combined with excessive losses through the digestive tract from diarrhea or through the kidneys from diuresis.