Only works in Singleplayer/Lan.

Change the difficulty to Relaxed. Now restart the game and change the difficulty to Brutal. Now DON'T restart the game. Beat Dracula on Relaxed difficulty and once you are able to extract his blood don't do it for now. Instead, restart the game. It should be in Brutal now. Quickly check it in menu and if it's correct, go ahead and extract his blood. The achievment only pops once the blood is extracted, not when the boss is defeated.