OMG!!! What a scary thing to have happen! Maybe it was making the fleas go crazy which in turn made the kitties get all itchy. At least that is all I hope it is! I'm glad you got it off of them and they are doing better now.
I only use advantage but I have tried the other over the counter stuff before. I don't use it anymore mainly because it didn't work. Thankfully my cats didn't react like yours did.

I'm so glad you rescued that poor baby! You are so right about getting a little kitten and then just leaving it outside!! Thats mean and it must have been terrified.
Can't wait for pictures!