Milk of Magnesia
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Image:Philipsmm.jpg Milk of Magnesia or Milk of magnesia, Mg(OH)2 is a saline osmotic (hydrating) laxative. The name derives from the solution's milky white appearance and the magnesium in its composition.
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History
The term "Milk of Magnesia" was first used to describe a solution of magnesium hydroxide at about 8%w made by Charles Henry Phillips in 1880; hence, the brand name Phillips' Milk of Magnesia. Although the name may at some point have been owned by GlaxoSmithKline, USPTO registrations show "Milk of Magnesia" to be registered to Bayer, and "Phillips Milk of Magnesia" is registered to Sterling Drug.
Pharmaceutical uses
Available over-the-counter, it is most commonly used in alleviating constipation, but can also be used to relieve indigestion and heartburn. When taken internally by mouth as a laxative, the osmotic force of the magnesia solution acts to draw fluids from the body and to retain those already within the lumen of the intestine, serving to distend the bowel thus stimulating nerves within the colon wall inducing peristalsis and resulting in evacuation of colonic contents. It is also used as an antacid though more modern formulations combining the antimotility effects of equal concentrations of aluminum hydroxide to avoid unwanted laxative action have largely replaced this indication.
According to MedlinePlus Medical Encyclopedia[1] milk of magnesia is useful against canker sores (aphthous ulcer).
Biological metabolism
When the patient uptakes the milk of magnesia (orally), the solution enters the stomach. Depending on how much was taken during the uptake, one of two possible outcomes will happen.
As an antacid, milk of magnesia is dosed at approximate 500mg to 1.5g in adults and works by simple neutralization, where the hydroxide ions from the Mg(OH)2 combine with the H+ ions in the stomach (H+ ions are what forms acidic solutions) to form water.
As a laxative, milk of magnesia is dosed at 2-5g, and works in a number of ways. Firstly Mg2+ is poorly absorbed from the intestinal tract, so it draws water from the surrounding tissue by osmosis. Not only does this increase in water content soften the feces, it also increases the volume of feces in the intestine (so called intraluminal volume) which is a natural stimuli of intestinal motility. Furthermore, Mg2+ ions somehow cause the release of CCK which causes intraluminal accumulation of water, electrolytes and intestinal motility. Although it has been stated in some sources, the hydroxide ions themselves do not play a significant role in the laxative effects of milk of magnesia, as basic solutions (i.e. solutions of hydroxide ions) are not strongly laxative and non-basic Mg2+ solutions, like MgSO4 are equally strong laxatives mole for mole (Tedesco & Di Piro, 1985; Curry, 1983).
The magnesium salts from milk of Magnesia are normally excreted by the kidneys, however, in those with liver damage or people who are otherwise renally insuffient, Mg2+ ions can accumulate in the blood, causing hypermagnesemia.
Care should be taken with the use of milk of magnesia for either of these purposes, as it can easily cause diarrhea.[2]
References
Curry CE: Laxative products. In: Handbook of non-prescription drugs. 1983, 6th ed., pp. 69-92, American Pharmaceutical Association, Washington DC.
Tedesco FJ, DiPiro JT. Laxative use in constipation. American College of Gastroenterology's Committee on FDA-Related Matters. Am J Gastroenterol. 1985 80(4):303-9.Template:Pharma-stub