Zithromax antibiotic can be used for treatment middle ear infection, tonsillitis and strep throat. If you think you have developed any other infections while you are taking this medicine at the same time as magnesium-based antacids because antacids will bind the Azithromycin and prevent it from being absorbed from the intestine. Zithromax is a prescription antibiotic that is now available for buying online. Zithromax is an unusual antibiotic in that it stays in the body for a significant period of time after the required doses.