I am not a doctor, however this is what I found while searching the internet: “Do not take antacids that contain aluminum or magnesium within 2 hours before or after you take Zithromax. This includes Rolaids, Maalox, Mylanta, Milk of Magnesia, Pepcid Complete, and others. These antacids can make Zithromax less effective when taken at the same time.” Omeprazole doesn’t contain aluminum or magnesium, so I think you’re OK. (And remember to take the whole course of the antibiotic! Stopping in the middle will just make things worse later)