Why would you want to do this? Revolution kills every thing that Frontline does, plus it kills ear mites, mange, and round worms. These are very toxic chemicals you are dealing with – would you double dose a child with them? Of course not, so why even consider doing it to your dog?
Just use the Revolution once a month and forget the Frontline.
I feel grief for you. Are you sure they weren’t poisoned ?. You really need to get with the vet to find a cause and reason…even autopsy. I had a litter of cats die at one time and turned out to be rat poison by a neighbor. Listen to the previous vet and find the cause. I’m so very sorry for your loss. There is a reason and a cause. I wish you relief.