You don't need to protect from everything. Several of these issues are so rare that you're better off treating them than preventing them and your dog suffering side effects.

You should really just talk to your vet. There's way more to it than a simple chart. They know the pharmacology, effectiveness, and necessity of all these drugs.

My girlfriend is a vet, and our dogs only take Trifexis. It works for our animals, their lifestyles, and our part of the country. Her prescription might change for an animal with short fur that goes hunting a lot. It all just depends.

In addition to not needing coverage for everything, some of the treatments require prescriptions because they can be dangerous to the pup. An example is preventative heartworm medication can be devastating to a dog with heartworms. A blood test is done to make sure a dog is heartworm negative.

Not sure but some medication will interact negatively with others. Vets will usually tell you to give the heartworms medicine one day, and the flea one the next day, but not both at the same time.

My first idea was that some of the pesticides in different medications might block or interact with each other, which is the reason why you usually get conditioner and shampoo in two bottles (the chemicals in most conditioners are cationic while the ones in shampoos are anionic)

Having now looked through quite a few Wikipedia articles of the pesticides used, I can't find no such statements... Except that I learned that some of these have a vague link to CCD.

Another thing is that the application time-scale and use-cases between these drugs differs - some you give every 6 months or so as prophylaxis, some you only give when there's an actual infection.