I am not a vet, so I would call one to check with them before I’d do anything. A vet told me Benadryl was safe for dogs, one ml per pound. I also recently found out many OTC drugs can be very harmful or even fatal to pets, such as ibuprophen and acetaminophen (sp?-The drug in Tylenol), and since dogs and cats are two different animals, please PLEASE call a vet before giving your cat anything.
I will repeat the advice to call your own vet, a message board, the internet in general are not substitutes for proper medical diagnosis etc.
however, since some one has already mentioned the benedryl in the water, apparently (and this is why you should contact your vet), different forms have different effects on kitties it recommends a pill form. of course, all benedryl I’ve seen were in capsules, vs. pills, and may not be in the mg size you’d need (I’d tend to think not since the caps would be for kids 12 and up who would weigh substantially more than even a large kitty).
Don’t use OTC pain killers on cats or dogs. The resulting symptoms are very similar to those of strychnine in humans, including severe pain, hypersensitivity to light & sound, convulsions & finall DEATH!!!
One of our cats is alergic to something and pulls out his fur. Our vet has us give him half a tablet of regular strength bendryl. So while you can give it to your cat and not kill it, you really need to ask the vet how much, since ours is quite large(about 11 lbs), and it’s a tiny amount he is given; I’m sure it’d be very easy to overdose a small cat on the same amount.