Alginic acid is an acidic material in which the carboxyl group of uronic acid, the constituent sugar, is in the form of a free acid (-COOH).
Alginic acid is insoluble in water but becomes soluble when neutralized with alkali.
Medicinal tablets can be insoluble in the stomach but soluble in the bowels. To release the active medical ingredient properly in the bowels, tablets include alginic acid, a disintegrant, which swells in water.
Powders such as starch are commonly used but if alginic acid (a tablet disintegrant) is added, this produces tablets which show different properties from starch.
These tablets have a gastro resistance function as the alginic acid does not dissolve in the stomach acid and the tablets are subsequently delivered to the intestine.
Alginic acid begins to dissolve as the surrounding pH gradually increases in the intestine, where the tablets disintegrate and the active ingredient is released.
Alginic acid is important in designing tablets which are insoluble in the stomach and soluble in the intestines