Aliginic acid is a linear block copolymer polysaccharide. A property of aqueous solutions of sodium alginate is their ability to form firm gels on the addition of calcium ion~1. There have been many investigations of the use of alginate gels for the sustained release of drugs. However, there have been very few reports on the use of alginates in liquid sustained release preparations for oral administration~2. In this work we apply a similar strategy to that reported previously for the in situ gelation of gellan~3 in which gelaiton of a solution of sodium alginate containing Ca++ ions is delayed until the preparation reaches the acid environment of the stomach through complexation of the Ca~++ ions with sodium citrate. The method therefore differs from those previously reported~2 in that we include a source of Ca~++ ions in the formulation.
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