Adefovir impurities are the unwanted substances that may be present in a sample of adefovir or its formulations. These impurities can arise during the manufacturing process or storage of the drug and can affect the quality, safety, and efficacy of the drug. It is important to monitor and control the levels of these impurities to ensure the drug is safe for use. Analytical methods are used to identify and quantify these impurities to meet regulatory requirements.