Cats and aspirin?

Lord only knows what Jordan did, but his front right paw is swollen almost twice normal size. When we first noticed it this morning he wouldn't let anyone get a look at it. I thought maybe it was a bee sting so I gave him a dose of Regina's leftover prednisone to alleviate some of the swelling. The pred worked but Jordan's still being very careful with that paw. I have some large breed buffered aspirin for Titus. The dosage says to give half a pill per 30 lbs. I know that cats are sensitive to aspirin. What I need to know is how sensitive? If I give him a quarter of a tablet just to get him thru to our vet appt. in the morning is that going to cause more harm than good?