Magnesium excretion

Potassium-sparing by diuretic agents, particularly spironolactone, enhances the effectiveness of other diuretics because the secondary hyperaldosteronism is blocked. This class of diuretics decreases magnesium excretion, eg, amiloride can decrease renal excretion of potassium up to 80%. The most important and dangerous adverse effect of all potassium-sparing diuretics is hyperkalemia, which can be potentially fatal the incidence is about 0.5% (50). Therefore, blood potassium concentrations should be monitored carehiUy. 

Leary WP. Diuretics and increase in urinary magnesium excretion possible clinical relevance. In Puschett JB, Greenberg A, editors. Diuretics IV Chemistry, Pharmacology and Clinical Applications. Amsterdam Elsevier, 1993 261-5. 

Jorgensen FS, Brunner S. The long-term effect of bendro-flumethiazide on renal calcium and magnesium excretion and stone formation in patients with recurring renal stones. Scand J Urol Nephrol 1974 8(2) 128-31. 

Because absolute magnesium excretion falls as GER declines, serum magnesium concentrations rise in patients with moderate to severe renal insufficiency. Indeed, magnesium concentrations steadily rise as the GER falls below 30 mL/min." As long as the patient maintains... 

In some instances, particularly in humans, alleviating the underlying disease responsible for decreased magnesium intake or absorption, or enhanced magnesium excretion, will correct the... 

Another four patients, two men aged 63 and 81 years and two women aged 73 and 62 years, who had been using a proton pump inhibitor (esomeprazole, pantoprazole, omeprazole, or rabeprazole, 20-40 mg/day) for 1-13 years, developed severe hypomagnesemia with hypocalcemia, relative hypoparathyroidism, and extremely low urinary calcium and magnesium excretion [52 ]. One was admitted with postanoxic encephalopathy after a collapse probably caused by a dysrhythmia. The others had electrocardiographic abnormalities... 

The main route of excretion of magnesium is the urine. Aldosterone, a hormone secreted by the adrenal gland, helps regulate the rate of magnesium excretion through the kidneys. Losses tend to increase with the consumption of alcohol or the use of diuretics. 

Massey, L. K., Wise, K. J., The effect of dietary caffeine on urinary excretion of calcium, magnesium, sodium and potassium in healthy young females, Nutrition Research, 4, 43, 1984. 

Hypomagnesemia is usually associated with disorders of the intestinal tract or kidneys. Drugs (e.g., aminoglycosides, amphotericin B, cyclosporine, diuretics, digitalis, cisplatin) or conditions that interfere with intestinal absorption or increase renal excretion of magnesium can cause hypomagnesemia. 

Magnesium should be replaced over 3 to 5 days because 50% of the dose is excreted in the urine. 

The main inorganic components of the urine are the cations Na"", C, Ca "", Mg and NH4 and the anions Cl , S04 , and HP04 , as well as traces of other ions. In total, Na"" and Cl represent about two-thirds of all the electrolytes in the final urine. Calcium and magnesium occur in the feces in even larger quantities. The amounts of the various inorganic components of the urine also depend on the composition of the diet. For example, in acidosis there can be a marked increase in the excretion of ammonia (see p. 326). Excretion of Na C, and phosphate via the kidneys is subject to hormonal regulation (see p. 330). 

Pharmacokinetics IM injection results in therapeutic plasma levels within 60 minutes and persists for 3 to 4 hours. IV doses provide immediate effects that last for 30 minutes. Effective anticonvulsant serum levels range from 2.5 to 7.5 mEq/L. Magnesium is excreted by the kidneys at a rate proportional to the plasma concentration and glomerular filtration. 

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