Answer
Dustin Poirier has never defended his Interim UFC Lightweight Championship because he was defeated by Khabib Nurmagomedov in his first title defense. Poirier won the Interim UFC Lightweight Championship by defeating Max Holloway in April 2019. He was then scheduled to defend his title against Khabib Nurmagomedov in September 2019, but the fight was postponed due to Nurmagomedov's father's death.