We have always used Trifexis for Feebee. When we went to the vet this month to get her treatment we needed something for ticks also. So the lady talked us into getting Iverhart max to prevent worms through the summer months (while ticks would be out) and then Vectra 3D for fleas and ticks. Then we will go back to Trifexis when we do not have to treat for ticks. That would save us about $25 a month. So the next morning we gave Feebee the Iverhart max. We held off on the Vectra 3D. I didn't want to do both of them at the same time. By that night she was lethargic, her nose was running, she was salivating, had dilated pupils, and burping constantly. She was not herself at all. She had an adverse reaction to it and is allergic to the ivermectin that is in it. These symptoms got worse and lasted for about 48 hours. It was terrible. So she cannot have anything with ivermectin in it again. So we will have to go back to Trifexis or Sentinal for her heart worm preventative. Now I am worried about putting the Vectra 3D on her because she was so sensitive to the ivermectin. Has anyone ever had issues with their bully not tolerating it? If so, what problems did they have? Thanks in advance for your input.