Azithromycin and Doxycycline are both commonly prescribed for respiratory infections and STIs — but the 2021 CDC guidelines now prefer Doxycycline over Azithromycin for chlamydia, and Doxycycline is the only appropriate antibiotic for tick-borne diseases and acne. This complete comparison covers all 7 major indications, a full head-to-head table, and a clear guide on which to choose for your specific situation.