Why do the bottles of pedialyte say refrigerate and use within 48 hours after opening?

So you buy more: Pedialyte has the same pen shelf life as juice or sugar containing sports drinks would have. They want you to limit open use to 2 days for two reasons - first, you shouldn't be using this for more than a day or two for a baby/toddler GI illness without letting your doctor know, because your child should be evaluated if needed longer. Second, they are in business to make money and want to sell more.

Simple answer:: To prevent bacterial contamination. Before opening the liquid is sterile and this is not the case after opening to the air. Hope this helps.