Puppy killers

My kids got a new puppy last week. I noticed afew worms so we bought Harts ultraguard plus rid worm. The next day the pup was has playful by that night she wouldnt eat or drink. My first thought was parvo. We made a vet appointment and went to the store to buy pedialyte, roughly a hour after getting home the puppy died in my wifes lap. Sadly our story doesnt end there. At the same time we also treated our 6 month old st. bernard. For 2 days we have been feeding him pedialyte with a suringe and praying he gets better. Please spend the extra $ for a safe product. Had I known then what I know now! Our four legged friends are worth it.