My Shih Tzu had an adverse reaction to K9 Advantix II yesterday. It was the second time I'd applied it to him, which according to my vet is often when an adverse reaction occurs. Within two hours of application he got extremely itchy and like he couldn't stand to be in his own skin. So I gave him a bath in Dawn dish detergent and took him to the vet to be checked out. He was given a shot of Benadryl and we discussed another option for parasite control.
Does that mean I think K9 Advantix II is dangerous/bad/should be dissed all over the Internet? No. It just means it's not the right product for this particular dog. My oldest son adversely reacts to amoxicillin. Does that mean it's a bad drug overall? No. Of course not.