IBD will kill pythons very quick. It is a way people used to check for IBD carrying boas a long time ago. They would put a normal BP in with the boa in question and if the python died within a few days, you know the boa was a carrier or so I was told. IBD does act really fast on pythons though. I would call the vet as the snake might be having a reaction to the medicine as you said he starts to act weird 5-10 mins after the shot. The vet might need to see him again.

Also IBD is not that common. People like to throw it around like its mites or an RI but actually its pretty rare unlike other stuff that will give the same symptoms like poisons and overheating.