I am not a vet so take this info as my opinion and experience only.
We had two birds come down with a respiratory problem and our breeder suggested using Tylan 50 injectable. It is given in their left breast for 3-5 days 1/2 cc daily. It knocked whatever they had right out and they were showing improvements even the next day, and of course we treated the full 5 days.
I don't know anything about the antibiotic you were giving before, so maybe that is an even stronger drug than this, but I thought I'd mention it anyway.
We had two birds come down with a respiratory problem and our breeder suggested using Tylan 50 injectable. It is given in their left breast for 3-5 days 1/2 cc daily. It knocked whatever they had right out and they were showing improvements even the next day, and of course we treated the full 5 days.
I don't know anything about the antibiotic you were giving before, so maybe that is an even stronger drug than this, but I thought I'd mention it anyway.