Nexium and Prilosec belong to the same class of medications - both are known as PPIs and work in the same way. The Prilosec should still work for you.

If you notice that it's not working as well, you can talk to your doctor about switching back to Nexium. Often, insurance companies will have a list of "preferred medications" (such as Prilosec in your case). The insurance won't pay for similar medications (such as Nexium)  that are not on the preferred list until AFTER you try the one that is preferred. If the Prilosec doesn't work for you, the doctor may be able to get what's called a "Prior Authorization" for Nexium through your insurance. Not all insurance offer this option, though, so be aware that it might not be possible.

Best of luck,

Casey