It was written somewhere that for chlamydiosis use 250 gm Azithromycin + 0.25 oz Lactulose. Scheduled dose is one drop per gram body weight BID for 14 days. Please let me know same combination may work for respiratory tract infection.
being a man of pharmacology i did not find use of azithromycin in poultry it is mainly used in humans for treatment chlamydia, toxoplama , haemophilus @ RTI
Azithromycin is macrolids group, and mostly Tylosin is used from this group to treat CRD. Some countries have restrictions on what to use though.You can consider others as Erythromycin, clarithromycin . All those are bacteriostatic at low dose and cidal at higher dose.
You can also use Tiamulin Hydrogen Fumerate for CRD,
For more details refer to Merk veterinary manual please.A general rule is to combine Bacteriostatic antibiotic with Bacteriostatic AND Bacteriocidal antibiotic with bacteriocidal in order to achieve synergestic effect