Internal Antibiotics for Indian Runner with open wound?

I'd rather not give Icarus an antibiotic via injection, but I will if I must. He isn't quite a year old, last year's baby you know. He's a Fawn and White Indian Runner. He's quite tame, as far as males go. He has a large gash on the side of his neck, down on his shoulders really. It starts in the center between his shoulders and extends down approximately 180 degrees, thinking of his neck as the center. It's quite grusome, but he's beeing kept in a sterile environment with fresh food and healthy food. His wound will be cleaned and dressed a few times a day, including a topical antibiotic. What he needs now is an internal antibiotic, over the counter perhaps? I know Baytril works on respitory ailments, but would it work in Icarus' situation? What about Ornacyn? I've heard of that. Any something like....Tetramyicin? I'm sure I spelled that incorrectly. Anyway, I would be much obliged by any and all advice.