Pharmacology principles provide key understanding that underpins the clinical and research roles of nuclear medicine practitioners. Indeed, the scope of practice of the nuclear medicine technologist demands knowledge and understanding of indications, contraindications, warnings, precautions, proper use, drug interactions, and adverse reactions for each medication to be used. This article is the third in a series of articles that aims to enhance the understanding of pharmacologic principles relevant to nuclear medicine. This article will build on the introductory concepts, terminology, and principles of pharmacology explored in the first 2 articles in the series. Specifically, this article will focus on the pharmacologic principles associated with interventional medications encountered in renal and biliary imaging. A companion article (part 3B) will examine the less commonly used interventional medications in general nuclear medicine and prototype adjunctive medications. Future articles will address the pharmacology related to nuclear cardiology, the emergency crash cart, and contrast media associated with CT and MRI.