Healthy, natural pastures is very valuable for biodiversity in the form of both plants and animals. An efficient use of pastures helps to preserve biodiversity, but grazing animals needs to be de-wormed to keep them healthy and to prevent harmful parasites spread on the pasture. The awareness about the environmental impact of the frequent use of deworming agents is low among the public. Some people are unaware that the absorption in horses of anthelmintics is incomplete, which make the circumstances about enviromental effect important to investigate further. The scientific evidence in this area is limited and more studies and trials are needed to deepen the knowledge about the effects of anthelmintics in the environment.

Horses are herbivores that spend almost all day grazing. While grazing they are infected by different endoparasites through ingestion of infective eggs or larvae on pasture. The most significant equine endoparasites in Sweden are the equine roundworm Parascaris equorum, small (Cyathostominae) and large strongyles (Strongylus spp), the tapeworm Anoplocephala perfoliata and the pinworm Oxyuris equi. For many years have horses been dewormed on regularly basis, which has resulted in the development of resistance to many anthelmintic classes. Because of the problems with resistance it is since 2007 necessary to have a prescription on anthelmintics and faecal sampling is also recommended.

Bensimidazoler är en flitigt använd bredspektrumverkande substansgrupp antiparasitmedel. I Sverige finns det fem substanser (albendazol, febantel, fenbendazol, flubendazol och oxfendazol) som används inom veterinärmedicinen, varav en är en pro-bensimidazol (febantel). Däremot finns endast en substans tillgänglig inom humanmedicinen (mebendazol). Syftet med detta arbete är att reda ut skillnader och likheter mellan dessa substanser. Fokus ligger på kemisk struktur, kinetik, aktivitet, spektrum samt resistensläget i Sverige. Kemiskt sett är bensimidazoler relativt lika varandra då enbart substitutet (d.v.s.