Conversely, the kidney retains a strong capacity to resorb magnesium, and the main site for reabsorption is the thick ascending loop of Henle. Of these 3 types of diuretics, loop diuretics have the greatest effect on renal magnesium wasting because of their site of action. Prolonged administration of magnesium-free parenteral fluids may be a contributing factor. Prolonged nasogastric suction, infectious diarrhea, steatorrhea, inflammatory bowel disease, and GI neoplasms may cause hypomagnesemia. A congenital defect in GI magnesium absorption also has been described.
Several drugs can cause increased urinary loss of magnesium.
Magnesium deficiency is especially common in patients receiving furosemide diuretics. A congenital defect in tubular reabsorption of magnesium also has been described. Severe hypomagnesemia may occur during the recovery phase of diabetic ketoacidosis. Patients with diabetes who have chronically poor glycemic control may have a total body magnesium deficit, possibly caused by ineffective insulin-mediated cellular uptake of magnesium. Exact inpatient incidence is unknown.