We recently dewormed a litter of.shihtzu puppies with the Hartz ultraguard ridworm tablets. we dewormed 3 times over a 3.week.period as per the directions on the box. each time we.wormed the pups they passed a few worms in thier.stool and seemed to be fine afterwards but the last.time we wormed them one of the pups became violently.ill almost immediately. she began to vomit. she had diarhea and became listless and weak. not thinking that the wormer was to blame we assumed she had.parvovirus. and were.quite.panicky. we discovered afterwards.that the symptoms.she.was.experiancing.was.a reaction to the main ingredient in the wormer. a drug.called piperazine citrate. piperazine is commonly. used to deworm pigs and cattle. and is toxic to dogs it causes severe diarhea vomiting. siezures and in most cases death. there is nothing a vet can do other than give the dog charcoal and hope for the best. we lost the puppy and discovered that it didnt even get rid of the worms after 3 treatments our pups were infested with roundworm.