Revolution Rash

I put revolution on the back of my cat's neck 9/1. Today I noticed he is missing fur and has red scaly patches on the two places I put the revolution. Is this an allergic reaction? It almost looks like burns where I put the (vet-bought, non-expired) meds.

Likely it is a allergic reaction... I would get the cat to a vet ASAP

Well, I find this interesting. I Revolutioned the 6 housecats on 8/5. All 6 lost their hair where I put on the Revolution. I could buy one or two having an allergic reaction, but all 6 at once? I got it from the sample vet, who I trust completely. They said they did not change anything. I did not overdose...

A couple of times my cat has lost a bit of hair right after I apply spot flea treatment (Advantage or another brand). There isn't any change in the skin, though... it still looks pink and healthy.

It does make me nervous, but it happens rarely and he seems to have no other side effects.