Instruct: Classify the given Amazon review into positive or negative sentiment.
Query: No longer works

This stuff worked well a few years ago but doesn't anymore. The fleas in the southeast U.S. seem to have developed a strong resistance to it. We have four cats. Three of the cats were treated with Frontline Plus and one with a sample of Revolution we got from our vet. The Frontline cats were still scratching a week later while the Revolution cat was not. I really wanted the Frontline to work because it costs a lot less, but it didn't. I even applied a second dose after two weeks that still did not kill the fleas. And yes the house had also been treated. So I went to the vet after four weeks of Frontline Plus not working and and spent the big bucks on Revolution. All four cats are now flea free again. I'm not doing this as a free plug for Revolution, I'm just saying Frontline Plus no longer works and the manufacturer doesn't seem to want admit it or improve the formula. Just my two cents worth. Thanks for reading.