Kidney magnesium excretion

Extra magnesium may be required by individuals with conditions that cause excessive urinary loss of Mg, such as chronic malabsorption or severe diarrhea. Certain medications can also cause the kidneys to excrete excessive Mg, such as diuretics, and Cisplatin, which is used as a chemotherapeutic agent for cancer, as well as certain antibiotics. 

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. 

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. 

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. 

Pharmacokinetics Approximately 1 % to 2% of total body magnesium is located in the extracellular fluid space. Magnesium is 30% bound to albumin. With IV use, the onset of anticonvulsant action is immediate and lasts approximately 30 minutes. With IM use, onset occurs in 1 hour and persists for 3 to 4 hours. Magnesium is excreted by the kidney. 

Renal function impairment Because magnesium is excreted by the kidneys, parenteral use in the presence of renal insufficiency may lead to magnesium intoxication. Use with caution. 

The most potent type of diuretic, loop diuretics are named after the loop of Henle, a component of a nephron. The nephrons are the filtering units of the kidney, and are responsible for moving fluids and waste out of the bloodstream, resulting in urine formation. The loop of Henle is a branch within each nephron where sodium and potassium are reabsorbed back into the bloodstream instead of being filtered into the urine. Loop diuretics inhibit this action and promote excretion of the sodium and potassium instead, along with calcium and magnesium. Since excess sodium causes excess fluid build-up, this results in fluid loss. Furosemide (Lasix), bumetanide (Bumex), torsemide (Demadex), and ethacryinic acid (Edecrin) are all loop diuretics. 

The major ions in different organs and body fluids of euryhaline fish have been studied by a number of authors. The concentrations of sodium, potassium, magnesium and chloride were usually more concentrated in fish taken from sea water than in those from fresh water, the effect being shown in blood, kidney, liver, various secondary muscles and urine. The trend was less clear in the case of swimming muscle, as were the values for calcium (reviewed by Love, 1970, Table 30). All the ions mentioned above were much more concentrated in the urine of the fish from the sea, urine being one channel by which these salts are excreted. A fish with remarkable ability to control its internal milieu is the tilapia, in which the total sodium in the body increases by only 30% when it is transferred from fresh water to doublestrength sea water (Potts et al., 1967). 

The primary organ for the regulation of sodium, potassium, calcium, and magnesium is the kidney. An intricate series of physiological sensing elements and hormonal response mechanisms maintains homeostasis. A variety of diuretic drugs can be used to enhance urinary output of various soluble salts, primarily sodium and potassium chloride. Profuse sweating is also a pathway of excretion for soluble salts and occasionally zinc. ... 

Excessive urinary losses of magnesium from the kidneys are important causes of magnesium deficiency. Clinically important causes include alcohol, diabetes meUitus (osmotic diuresis), loop diuretics (furosemide), and aminoglycoside antibiotics. Increased sodium excretion (parenteral fluid therapy) and increased calcium excretion (hypercalcemic states) also result in renal magnesium wasting. 

Maintenance of fluid volume, osmolarity, electrolyte balance, and acid-base status are aU regulated in large part by the kidney. Homeostasis of sodium, potassium, chloride, calcium, magnesium, and phosphorus is altered due to changes in urinary excretion that occur in patients with impaired kidney function. A comprehensive discussion... 

While alcohol abuse may be associated with a variety of electrolyte and acid-base disorders, the role of the kidneys in this process has only recently been fully defined [164]. Renal functional abnormalities have now been related to chronic alcoholism in patients without liver disease and these defects have reverted to normal with abstinence from alcohol abuse. These abnor-mahties include decreases in the maximal reabsorptive abihty and threshold for glucose, a decrease in the threshold for phosphate excretion, and increases in the fractional excretion of P2-microglobulin, uric acid, calcium, magnesium, and amino acids. Defective tubular acidification and impaired renal concentrating ability... 

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