This cat NEEDS a vet ASAP, losing
5 lbs in
a week is very bad. That much weight
a week can be caused by many things-to name just a few-severe infection, kidney problems, poisoning, cancer, etc. And, if you do a yahoo/google search on weight loss in cats, you'll see a whole lot more. This is such a serious problem that there is nothing you can do at home that will cure him. You should do everything in your power to keep him inside and force feed him water and food.