What did Batman inject into his leg?

Pretty much. It's a deep dive into a comic story. A pretty good comic story actually.

With some chilling art, Batman actually fails to save the girl. It makes him nuts.

https://dc.fandom.com/wiki/Batman:_Venom

But at this point, he knew nothing of Bane. So it had to be something else. I thought it was just a shot of adrenaline.