Total loss of appetite

Question
My 5 year old cat Tyler has been suffering on and off for the past 10 months with Crystals in his urine.  He has been catheterised twice, the last time approximately one month ago. Since he has been home from the vet he has stopped eating.  He was 8.11kg and has now dropped to 6.8kg.  he has seen the vet twice in the last 10 days and she can find nothing wrong (did bloods etc)she has asked us to bring him back in 7 days if he does not improve.  I am now in total desperation as he shows no interest in anything, wont eat a thing or drink and the vet does not seem to be doing anything.  WE have started to try and force feed him but this is upsetting both him and us! In the last two days he has had about 2 tablespoons of wet food but nothing else.  I am my wits end as I cannot lose him.  Is there anything you can recommend?  Please help

Answer
Hi Susan!
I can completely understand your frustration and concern.
Has your cat been on a prescription diet for the crystals?  Hill's Science C/D is wonderful at maintaining the crystals from multiplying and Waltham's has a dissolution diet out.  I can't express how wonderful the Waltham's diet is.  My dog actually had crystals and bladder stones and this diet dissolved them, helping to avoid invasive surgery to remove the stones.  This diet may be of some help for your cat. These diets are prescription diets that are obtained by your veterinarian.
If your cat has not really eating in two days, he needs to be hospitalized, and on IV fluids.  Cats will quickly go into renal and liver failure if they do not have any food in their systems.  Waiting 7 days for a recheck at the vet is 7 days too many, in my opinion, and I would highly recommend a second opinion by another veterinarian....one that will do something for Tyler!
Is it absolutely proven that he is not suffering from a urinary tract blockage again?  Not eating/drinking, lethargy...these are signs of a urinary tract blockage, and even if you are seeing some urine in his litter box, he may be partially blocked.
The amount of weightloss is also of obvious concern, as you know.
It may be possible that his crystals have turned into bladder or kidney stones.  When crystals are present, they begin to attach to eachother as they multiply.  These crystals then begin to form stones. The most common crystal in cats is called a Struvite crystal or Calcium Oxylate Crystal.  These crystals/stones do respond well to antibiotics as well.  The only way to tell if there are stones present would be by a radiograph/xray.
With the information and the symptoms you have described, it sounds as though Tyler needs radiographs, antibiotics, Iv Fluids (he most likely is dehydrated by now)and supportive care.
I am unaware of what you would like to do for him financially, but there is a surgery called a "P.U." surgery that is performed on cats that block multiple times. The problem is that with male cats, these crystals get stuck in the tip of the penis, causing the urine to be unable to pass, hence causing a urine toxicity by all the urine that is stuck in the bladder, which makes the cat sick.  Catheterizing helps to get these crystals to pass, but if there is no special diet, these crystals are going to keep forming. The "P.U." surgery literally bypasses the urethra, making a different exit for the urine, this way the crystals will not get stuck in the tip of the penis. Because of your cat's history, this surgery may be a good idea.
I would definitely suggest a vet visit with another vet.  
Please let me know how Tyler does.  You may also want to try beef and/or chicken baby food as this sometimes increases appetite.