Magnesium salts have a variety of actions and uses. Magnesium is needed for normal enzyme activity, muscle contraction, and nerve condution. Magnesium ions prevents formation of renal crystalluria. The citrate ions render urine alkaline so that urates may dissolve and are easily eliminated. Also, citrate ions, by chelating calcium ions, inhibit formation of calcium oxalate. Therefore, magnesium citrate may be prescribed to prevent recurrence of calcium oxalate kidney stones. Magnesium citrate is an osmotic laxative.