Most grazing ruminants are infected by a variety of helminth parasites that have a massive impact on their health, welfare and their production. In that context, diseases caused by gastrointestinal nematode parasites are important animal health issues. The main mean to control such parasites relies on the use of anthelmintic drugs. However, intensive use of chemicals has selected drug-resistant parasite populations in many animal species. This includes resistance to the latest developed broad-spectrum macrocyclic lactones (MLs) such as ivermectin (IVM). There is now considerable evidence that the induction of detoxification systems upon exposure to IVM is an important step in the development of drug resistant organisms. In the nematode model Caenorhabditis elegans, we have generated an IVM resistant strain by drug pressure selection, called IVR10. In IVR10 worms, a battery of genes encoding proteins of the drug detoxification system are overexpressed, including several P-glycoproteins (Pgp) and cytochromes P450. Since Pgp-6 and Pgp-9 expressions were among the most increased in IVR10 strains, we first focus on these 2 proteins. Using CRISPR-Cas9 genome editing, we have generated stable IVR10 strains deleted individually for Pgp-6 and Pgp-9. This strategy allowed us to obtain 2 original stable strains fully deleted for individual Pgp on the IVM-resistant background. We have then compared IVM efficacy in these strains, in IVR10 and in wild-type worms by monitoring the drug impact on different phenotypes such as larval development, pumping and motility. This work allowed us to determine the putative role of individual Pgp in IVM resistance. It will provide new targets to improve IVM-based treatment