Instruct: Classify Amazon reviews into positive or negative sentiment
Query: zeb

I have used Frontline on my Golden for the last seven years with great results until this year. I put it on him and two weeks later he had fleas! I called the vet and they said I could apply it every two weeks. I put it on four times in eight weeks and he still had fleas!! I called the vet and ended up buying pills (3) for $51.00 and the first pill took care of the problem! Has Frontline changed the formula?? It doesn't work like it used to!!