2 Males used to be BEST buds now not getting along

Shiva my 6 year old Tuxedo cat has been living with Giddeon my 8 year old orange tabby since he was a kitten. Recently Giddeon developed struvite crystals and was brought to the vets. Upon his return Shiva was hissing and growling (if that is what we call it in cats) at Giddeon. Unfortunately Giddeon had to go back to the vets and spend a night and again upon returning was greeted with more hissing and yowling. Siiiigh. I realize Giddeon smells different and also the fact that he is on meds might be the contributing factors. I have done the Feliway spray and ionizers. Separated them and allow them monitored time together. They WILL not eat at their regular feeding place together so I feed them separately. I tried the on each side of the door thing and all Shiva would do is hiss and neither would eat. I couldn't have that so now I feed them far away from each other. I finally called my vet and told her it did not seem to be improving in fact Giddeon was now beginning to look at Shiva as prey and was giving off the vibe that he was seriously considering pouncing on Shive. The vet ordered some kitty Prozac to chill him out. It has been only 2 days. OK here is where it takes a turn for the worse. So far just mutual hissing and some growling from Shiva. Today they went nose to nose for a good 5-6 secs with no hissing. Then 5 mins later Shiva turns away to go into the bedroom and Giddeon pounced on him. We yelled and clapped our hands and it stopped. About an hour later Giddeon snuck into the bedroom to,quick for me to catch him and he did it again! Siiigh. So I gave him some kitty prozac tonight also. I am beside mysef and my nerves are shot. Am I doing the rightnthings? Is it going to improve. Is there something else I could be should be doing? Some sites say get out then catnip for play time others say NO because it makes them more aggressive. I totally switch rooms daily and from early day and evening so theynget plenty of each others scent. They are both using the 2 diff litter boxes. I just don't know what to do. I cannot imagine having tomgive one away if this does not stop. Oh I also bought and put on each of the calming collars tonight. Please anyone if you can tell me anything to add insight or hope that they will once again be laying on the couch next to eac nother lovingly I sure would appreciate it. Thank you so much Janet.

My suggestion would be to totally separate them while Gideon is being treated,  The stress of looking over his shoulder is going to make him worse, and if he acts like prey because he's afraid, then Shiva will attack him.  Rather than site swapping at this point, I would give Gideon he own SAFE room that Shiva is not allowed to enter, with his own box and food in there.  Do not let him have the run of the house unless Shiva is locked up somewhere ELSE.   When Gideon is done with all the vet visits and the medicine that makes him smell strange, bathe BOTH cats (so they will smell the same) and then start re-introducing them slowly, just as you would if you had a new cat.  I believe the first upset was caused by the smells coming from the vet's office, but after that, Gideon felt threatened so his behavior changed, he is now projecting fear, and Shiva eill take advantage of that.  You just need to undo it all and start over after Gideon is no longer sick.  In the future, if one has to go the the vet, you can always put a little dab of something very strong smelling on the nose of the other before letting them together and that will block the unfamiliar smell.  Waiting a day before letting them together also would be a good idea.

OK thanks. I have never bathed them what domyounuse?
Also If I give Giddeon the sheltered bedroom and Shiva the run of the house then Shiva just batts atbthe door and meows,to,get in. Imactually think Shiva feels safer in the bedroom.
Whadaya think? Thank Janet

Also it is Shiva that honkers down and slithers around while hissing. Giddeon has begun to treat Shiva as prey. I think Shiva is the one that is scared of Giddeon and now Giddeon is chasing or pouncing.

OK, that makes some sense.  Perhaps give SHIVA the sheltered bedroom and GIdeon the run of the house for now, and let Shiva out when you hae put Gideon away somewhere for awhile.  I do have one cat that several of the girls consider "prey" and he even runs when the little kitten chases him wanting to play.  And when he is stressed, he poops beside the litter box and pees wherever I will step in it and fall down, so I'm highly motivated to keep him feeling as safe as possible.  I have determined what cats he can share the house with, and when the problem ones are confined elsewhere, he can enjoy the house.  If one of them should slip out of her room, he makes a beeline for the bedroom, which is HIS safe room.

Ok thanks. What do you bathe your cats with? Something from the store? or just pet shampoo and a washcloth?

I use Bio-Guard manufacturerd by Farnham Pet Products.  It doesnt remove any flea protectoin you hve on them.  forgive y crappy typing but I am on the way out, just wanted to answr your questioon quickly.  I have a whole article on bathing cats  PM me later if you would like a copy, no time right now. 

Sure send it to me later. I called several pet stores and no one carries the Bio-Gard. I am on line with the Farnham Pet company now. They are looking for a local retailers for me. They mentioned both Walmart and Kroegers or Fryes Oh and they just added PetsMart and Petco. So I will go check that out.
Thanks again Janet