Yup - my Toller's reaction to it got worse and worse - the last time his behaviour changed for several hours and I was v worried
My vet thinks he's reacting to something in the liquid carrier rather than the drug itself iyswim so we've given up on spot owns and switched to a seresto collar backed up by milbemax to cover him for lung worm
Our lab does have a mild reaction, seems to zone out a bit and just looks at us as if he's a bit confused. Its times like this I wish they could talk so I knew if it was just a mild reaction or if the reaction is really bad for him.
My mums cat is allergic to all the spot ons - he acts bizarrely and turns pink ( he's a white/grey cat so you can see his skin colour) ,we are at the stage now that he has to have anti histamine before he has his vaccinations .