This clinical trial is focused on studying a kidney disease called Immunoglobulin A Nephropathy (IgA Nephropathy), which can lead to a gradual loss of kidney function. The study is testing a treatment called atrasentan, which is taken as a film-coated tablet. The purpose of the study is to evaluate how well atrasentan works compared to a placebo in reducing the amount of protein in the urine, which is a sign of kidney damage.

Participants in the study will be randomly assigned to receive either atrasentan or a placebo. The study is designed to be double-blind, meaning neither the participants nor the researchers will know who is receiving the actual medication or the placebo. The study will last for a period of time, during which participants will have regular check-ups to monitor their kidney function and overall health. There is also an open-label extension phase, where all participants can receive atrasentan to further assess its safety.

The main goal is to see if atrasentan can help reduce protein levels in the urine and slow down the progression of kidney damage. Participants will be closely monitored throughout the study to ensure their safety and to gather information on how the treatment affects their condition. This study aims to provide valuable insights into the potential benefits of atrasentan for people with IgA Nephropathy.