Alvimopan is a medication used to treat bowel problems after surgery. It is important to ensure that the drug is pure and free from any impurities. Alvimopan impurities refer to any unwanted substances that may be present in the drug, which can affect its safety and effectiveness. These impurities can arise during the manufacturing process, storage, or transportation of the drug. It is crucial to identify and quantify these impurities to ensure the quality and purity of the drug.