Very good. I know feed stores often sell antibiotics. Glad you got some help.
Meanwhile, I would give him some poultry vitamins to boost his little immune system. Poor guy. Things can happen.
How about putting a tablespoon of apple cider vinegar per gallon of drinking water? It is supposed to be a tonic, and have some mild antibacterial properties. I know it's not going to be in his bloodstream, but if he clears his nostrils with it it could help a little bit.
By the way, what is his drinking water source? Can he wash his head frequently?