Bruce didn't understand, he didn't realize the injector was in his wrist. He didn't even touch it besides ripping it out of his arm. One moment he was investigating the remains from weeks ago left in one of Hugo Strange's lab, mainly ashes and a few objects.

He thought it was throwing him off balance at first or making him hallucinate. Things felt like they were in slow motion, the hunger of half a dozen starving athletes,  and when he tried rushing to places he ended up across the room slammed into a wall. He asked Lee to Check him out but all she could say was that his heart rate, and metabolism was increased. He started started to enjoy the wind on his face, at inhumane speeds a blur responding to emergencies.  He went to Lucius for two reasons, his clothing was wearing thin catching fire  and the substance was running low. Lucius wanted him to be careful, but he knew the man wouldn't truly understand. Bruce felt like he was more than he was supposed to be inside, his voice slipping in a distorted tone. Even okay with what it did to his eyes.

Bruce kept zooming all over gotham, he didn't want to pump the breaks or hold back for a second. He wished he could have stopped the one moment he tried slamming Jonathan Crane's follower against the wall. Going so fast she destroyed the person on impact, blood all over him. Like a fly that hitting the windshield, Bruce couldn't even look in horror at the start when it kicked in. He was spitting out someone's molars and blood he swallowed by accident.

He told Jim, he told Lucius and tried to stop slowly. He kept seeing the blood on his hands, the voice in him and the impulses to do it again. But when Selina was paralyzed by Jeremiah he rushed out, trying to run again. To be faster than ever, he didn't even know how he did it but he ended up before it happened. He wanted to give this strength to himself, to stop it from happening.  Injecting him only to realize something was catching up to him, a trial of blue and he felt like he was on fire. It was burning,  it was overwhelming and then he felt nothing at all.