I had a cat die because of a sensitivity to Piperazine. I had used the product in the past for de-worming many ferals with no problem, but that one death taught me to stay away from the OTC products.
You can get Droncit and Drontal online which is what the vets use. Drontal is an all wormer that covers Round, Hook and Tape. Droncit is for Tape only. Panacur is an all wormer that vets also use when there seems to be a particularly resistant infestation.
My vet is aware of the products I use to treat and has given her blessings. She has me use Revolution flea treatment, (which covers Round, Hook, Mites and Heart), monthly, so the only worms I generally have to watch for anymore is Tape.
I recommend avoiding any products with Piperazine in them.