Male Cat with FLUTD, wet food intake

Hi, I've been writing all about our male cat Harry's medical problems on the Cat Health forum, but since he is home for now, I'm hoping you can

help me with his nutrition.  We live in Ireland. 

He has FLUTD and just got out of hospital today after weeks of being diagnosed.  The catheter just came out last night.  He's still on antibiotics/anti-inflams. 

Have read lots of posts and will keep him on an all wet food diet. He weighs 10 lbs 3 oz (4.7 kg)   Until Monday night, I am giving him Royal Canin C/D.  Vet said 

to then give him Hills (out of stock today)

They said 1 and a half pouch in morning and same amount again at night.   The poor guy is really, really hungry.  

Prior to being so sick the past 3 weeks,he ate one pouch of Felix and a little dry food in the morning----a little dry during the day, but not much---at night a little hard before he went out.

Maybe he wasn't getting enough in the hospital? Or maybe all the medicine he is on is making him hungry?

So far he hasn't used the litter box at all today since leaving the Vet....about 8 hours ago.  That has me worried, but if he does go during the night, would I give him more food than the 

1.5 they said to give him?

This is going to be a journey to get him well, so thank you for any advice. ..  

I'm not sure why they're telling you to limit food? Sometimes cats recovering from an illness don't have a good appetite or are nauseated, but if he's hungry I'd give him more food. Def agree he should be on a 100% wet food only diet. 

I am right there with you. Our boy (2nd one in 2 yrs) just came home Tuesday and HATES the c/d they sent home with us. I have tried a couple other urinary-health options from the pet store, and the only one he eats is the Purina at this point. I do add a bit of water to it when I give it to him, but the vet told us with the c/d to give him 2 of the 3oz cans a day - for a 15lb cat? I have been giving him 3 a day right now, because he was crying for food the first night so I fed him again. He is on no dry food, so I don't know how they expect him to maintain his weight with so little.

You can add any REAL MEAT to his food, whether cooked or raw, because real muscle meat has L-methionine which will keep the urine acidic. That's what the prescription foods are designed to do, only they do it by adding chemicals rather than by reducing the unnecessary fillers like corn, soy, grains and starches. Any of the pate variety canned foods that have no corn, wheat gluten, soy, peas, sweet potatoes or any of those non-meat fillers will add calories without adding carbs. My FLUTD cat has done fine for 1 1/2 years eating Friskies pate, Sheba pate, 4Health [Tractor Supply Company brand grain-free Chicken (NOT the kind with gravy!!) and Abound [Kroger brand] grain free turkey & giblets.