I have been using Vectra for fleas and ticks for the dogs. Well I ran out of it for the dobes. I have a couple of applications of Advantix that I found so I want to use those up. My concern is regarding my small dog. I have Vectra for her but will there be interactions if I use that on her and Advantix on the big dogs? They don't even play with each other so it's not like they would be touching each other or anything. Anyone know if this is safe to do? My vet isn't in the same town and I'm not feeling well and my hubby is out of town so I couldn't get over there to get any for the dobes until next week.