You won't find mixing Tylan with penicillin in a book though. I came up with that because I wanted to give Tylan for infections and it kept killing the tissues. I would give it orally to birds and they would die and when I looked it had burned their throats. But the medication is so good with the illnesses that my birds had I started trying to figure out how to do it differently so I didn't have it killing tissue. I started adding it to drinking water with astounding results. It worked so well I have continued to do that. Then I had some birds that would not get well I doctored them and doctored them and they stayed sick so one day I said I have to do something different. I could see black places on them from the tylan injections and I wasn't sure that wasn't making them sick too. So I mixed the Tylan with penicillin and gave it in shot and everyone got well very quickly. I have done that ever since. For some reason it does well together. By mixing it I quit have such tissue destruction in my birds too from it and it seems to work better. Tylan covers respiratory extremely well, it helps SOME diarrhea infections and I don't feel it gets too much in the tissues but penicillin does. Problem is there is just so many bacteria that is immune to penicillin anymore so some other ones may work better. Penicillin is an old medication that has been around a long time and it can have bacteria that have built up a resistance to it. I learned this taking care of my flock and thought I would share it with you guys. I hadn't been on Backyard Chicken for a while, I am printing your medication dosages and going to put them in my cabinet that is good information.