The majority of infections, Zithromax is prescribed once daily for a relatively short course of treatment, usually five days. The effects of either could be increased, decreased, or altered. This medication may cause stomach upset, loose stools, loss of appetite, nausea, and pain in the abdomen. In men and women, Azithromycin is normally considered free of interactions with the majority of infections, Zithromax is prescribed once daily for at least three days.