I have a couple of suggestions. The first one, talk to your vet first. If the Miralax isn't doing it's job, ask about giving him some Magnesium Sulfate. Basically, epsom salt and water. It can cause diarrhea, but other than that it is safe, so talk to your vet first.
Next is Dr. Elsey's Ultra Cat litter. It is a clay, hard clumping, 99% dust free and is supposed to be safe if your cat ingest it. It's pretty cheap, only around $20 (usd) for a 40 lbs bag. Give it a try.
Next is Dr. Elsey's Ultra Cat litter. It is a clay, hard clumping, 99% dust free and is supposed to be safe if your cat ingest it. It's pretty cheap, only around $20 (usd) for a 40 lbs bag. Give it a try.