The paper deals with three different groups of antiparasitics for use in dogs and cats from a toxicological point of view: phenylpyrazoles (fipronil), macrocyclic lactones and pyrethrins and pyrethroids, which are administered to pets in a way and in doses that are not recommended or if the animal comes into contact with them in any other way, they can cause poisoning. For each mentioned active substance, the method of use, toxicity, pharmacokinetic data, mechanism of action, clinical signs, diagnosis and therapy of poisoning are described. The choice of an antiparasitic preparation primarily depends on the type of parasite and its stage, but also on the animal species, individual differences of the organism in terms of age, condition, breed and certain genetic predisposition. If the specified parameters are not taken into account when choosing antiparasitics, their use can cause toxic effects in animals. All processed antiparasitics in the work show a high degree of selective toxicity for the target species of parasites compared to other animals, which are based on different mechanisms. Pets of certain species and breeds are extremely sensitive to poisoning with processed antiparasitics, for various reasons. Treated antiparasitics in the case of poisoning of dogs and cats primarily cause disorders in the work of the nervous system. There are no specific antidotes for the above poisons, therapy regularly begins with the decontamination procedures of the poisoned animal, followed by symptomatic and supportive therapy. Demonstrating the toxic effects of fipronil, macrocyclic lactones, and pyrethrins and pyrethroids in pets as a consequence of the use of ready-made antiparasitic drugs is a way to warn of the importance of proper handling and application of said drugs by both animal owners and veterinary doctors.