Magnesium is the fourth most common cation in the body and the second most abundant intracellular cation after potassium. Magnesium plays an essential role as an enzymatic cofactor in a number of biochemical pathways, including energy production from adenosine triphosphate (ATP).
Magnesium has a direct effect on the Na+/K+-ATPase pump in both cardiac and nerve tissues. Further, magnesium has some calcium-blocking activity and may indirectly antagonize digoxin at the myocardial Na+/K+-ATPase pump.
Magnesium modifies skeletal and smooth-muscle contractility. Infusions can cause vasodilation, hypotension, and bronchodilation. It can reduce or abolish seizures of toxemia.
Magnesium is primarily an intracellular ion, and only 1% is in the extracellular fluid. A low serum Mg level (<1.2 mg/dL) may indicate a net body deficit of 5000 mg or more.
Hypomagnesemia can be associated with a number of acute or chronic disease processes (malabsorption, pancreatitis, diabetic ketoacidosis). It may result from chronic diuretic use, cisplatin administration, or alcoholism. It is a potentially serious, life-threatening consequence of hydrofluoric acid poisoning.