Reaction or just a coincidence?

Is it possible to have a reaction to other injections - not just a vaccine?
I have heard of a dog developing a lump on the site of an anti-biotic jab. What could cause that? Is their any other ingredients in an antibiotic jab that a very sensitive animal could have a reaction to? Or could the antibiotic itself set off a lumpy reaction? Or could it just be a coincidence?