Hi. I had a female tabby cat who was fine until she was around 10 years old. Then she suddenly began having constipation issues and would cry and hide under the bed. Her little butt was all red and swollen and she was straining and licking at it. Long story short - after years of help from the vet, which really didn't do much for her at all (pumpkin, laculose, manual extraction - you name it) I read online at a Yahoo forum on the subject, about giving Miralax sprinkled dry on the wet food each day. She never had an issue again unless I stopped. She lived to be almost 20. Now I have a cat who used to be feral and he can go for over a week without pooping. He never drinks water! I tried all the usual remedies listed here, and the aloe juice did nothing! Anyway, I'm back on the Miralax for him which works 100% and there is no taste. I don't want him to end up with megacolon like my little tabby, so if this is what it will take, I guess that's what I will do. I feed him a raw diet which I make myself. I am told he is extremely healthy otherwise. My recommendation - use the Miralax. It seems so unnatural, but if the cat gets megacolon, it's a horrendous situation.
The cat I recently lost after 19 years got diabetes when she was 11 or 12, but it was controlled by using a wet canned food with no sauces, high protein and under 10% carbs. But when she was 17 she got kidney failure. While there is basically no meds in Sweden for treatment for cats with kidney failure I joined an on line group and they helped a lot. These cats often have constipation. Miralax is not sold or allowed in Sweden but I got it into the country. She got about tsp 2 times a day. I began with 1/8th of a tsp and just added to it until her stool was good. It works well. The only thing they have here is a paraffin wax that is liquid and the cat gets it but it coats the stomach so NO food is digested it just passes on through with no nutrition.