Increasing the use of anthelmintics for veterinary and other medical therapeutic purposes leads to their continuous and uncontrolled release into the environment. Although pharmaceuticals and their metabolites are found in traces, they can lead to high long-term concentrations and therefore have a detrimental effect on the environment. Since their chemical resistance, accumulation potential, microbial resistance and synergistic effects are not yet fully known, it is necessary to develop and apply analytical and bioanalytical methods for the detection of anthelmintics and their degradation and/or transformation products. The aim of this study was to examine the biodegradation efficiency of the anthelmintics mebendazole, albendazole and febantel, and their mixture. The biodegradation process was carried out in three aerated batch reactors of different contents. The first reactor was a control reactor containing only the working solution of the test pharmaceutical at a mass concentration of 3 mg L^-1. The addition to the second reactor is activated sludge, while in the third, in addition to all the above, a known mass of microplastics was added. In addition to examining the physicochemical parameters of biodegradation, monitoring the concentration of anthelmintics at defined sampling intervals, the ecotoxic effect of individual components and their mixture was assessed. In this study, biodegradation of anthelmintics with activated sludge with a mass concentration of 4 - 5 g L^-1 was achieved. It is assumed that in addition to the main mechanism of antiparasitic removal - biodegradation, hydrolysis, and adsorption on the floculae of activated sludge are also occuring. The parameters monitored during biodegradation were pH-value, room temperature, temperature of each reactor and the remaining working volume of the solution in the reactor. The newly formed degradation and/or transformation products were detected by high performance liquid chromatography. The toxicity of the selected investigated anthelmintics and their mixture after biodegradation was also assessed using the bioluminescent method of determining acute toxicity with bacteria Vibrio fischeri.