Cat refusing to use litter box

Question
A little history... about a year ago and again about three months ago my cat (half siamese, half unknown) had a urinary tract infection for which he took medication and it got cleared up.  Also, about a year ago we moved to a new house.  Since the second infection, he refuses to use his litter box.  He is 12 years old and has never exhibited this behavior prior to this. He is currently using various corners in the house and urinating on the carpet.  He deficates right in the middle of the floor on the carpet.  In order to try to stop this behavior I have enclosed him in a part of the house that is all ceramic tile flooring (hall, laundry & bath) with his litter box, food, water and bed.  It has now been over 36 hours and he has not urinated.  My question is this, could I be doing him any harm by allowing him to go this long without urinating?  Thanks for any help you can offer.

Answer
Hi Connie!  Generally, 36 hours of not urinating is a bit alarming.  Male cats have a tendency to develop a urinary blockage, so this always becomes a concern when a male cat does not urinate for a long period of time.  Boycotting the litterbox can be caused by a few things...urinary tract infection (as you know),stress (perhaps this is a behavioral issue because of the stress of your new home?), and even him not feeling his best from another unknown ailment (it's very common for cats to not use the litterbox when feeling ill).  You may want to have your veterinarian perform a physical examination on him to rule out any health related problems.  Since he has had two urinary tract infections(UTI's) pretty close together, the antibiotic for the last infection may not have been strong enough to kick the entire infection out.  Clavamox is usually the antibiotic prescribed for a UTI, but sometimes, the antibiotic called Baytril (which is much stronger) is needed if there is a lingering infection, which your cat may be experiencing.
I wish I could be of more help.  Please keep me posted and let me know how he does!
Hilary