Nitrogen containing, 15 membered ring called azalides. Act against H. influenza, M. catarrhalis, M. pneumoniae> 5 day dosing for respiratory tract infections Stability to acid catalyzed degradation Increase lipid solubility Taken 1 hr before or 2 hrs after meal Food ↓ absorption PROLONGED HALF-LIFE UP TO 5 DAYS. MORE ACTIVE AGAINST GRAM NEGATIVE. ONCE DAILY DOSING.