I give Racci 1/4 tsp. bid of Miralax every day because she is always constipated. She's an old lady and big, about 19 lbs. Depending on size and how bad it is, you can give 1/8 to 1/4 tsp 2x daily of Miralax. It's very gentle and can't hurt kitty. Some ppl mix it in the food. I can't take a chance on it not being eaten because she gets so miserable or her smelling it or tasting it since I just switched her to wet food, so I premix it with water and give it by syringe, then give more water with her water bowl.
The vets recommend it, including our vet member, Dr. Lisa Pierson.
Melanie & Racci