Do slow releasing medicines like nexium stay in stomach undigested untill fully absorbed by body and do not pass down along with food or what?

Pill keeps moving: Slow release medications are made by making a layer of medicine then coating it with a membrane that needs to be dissolved, then another layer of medicine, and another layer of coating. In this way it slowly breaks down. The pill keeps moving through the intestines as it breaks down. If you break a pill, you ruin the slow release by breaking the layers.

If an orally admin-: interred drug harms the stomach lining or decomposes in the acidic environment of the stomach, an enteric coating can be applied to the drug to prevent it from dissolving until it reaches the small intestine. Other techniques are used that allow the active ingredient of a drug like Nexium to be released slowly or in small amounts over time, usually 12+ hours, mostly in the small intestine.