Miralax (or its generic equivalent): Again, it increases fecal water content without adding bulk to the stool. Most feline veterinary practitioners like using Miralax much better than lactulose which also adds water but not bulk. Miralax is tasteless and can be mixed with the food. This is much better than trying to get sweet, sticky lactulose into a cat!
Start with 1/8 tsp once or twice-daily mixed into the food and increase from there to get the desired fecal consistency. Most cats do well on no more than 1/4 tsp twice-daily but it is safe to go higher. If your cat’s stools are too loose, lower the dosage.