The Deadly Experiments of Dr. Eeek by R.L. Stine

Top secret and dangerous. That's what your mom, a famous scientist, calls the research she's been doing at the labs of Dr. Eeek. You're dying to know what its all about. Then one day you get lost in the labs. Before you know it, you've become a human guinea pig in Dr. Eeek's deadly experiments! If you choose one lab, you meet a dog wearing sneakers. He's half dog half kid. If you choose another lab, you get lost in a maze which happens to be the home of an enormous rat.