Which of the following correctly describes the distinction between an in vivo nonclinical study and a study using cell cultures?

• A. An in vivo nonclinical study focuses on a living test system, whereas a study using cell cultures is in vitro
• B. An in vivo study uses artificial models only
• C. In vitro studies involve animals
• D. In vivo studies are not part of GLP

Answer: (A)

You're being asked to distinguish between studies done in a living system and those done in cell cultures. An in vivo nonclinical study uses a living test system—typically a whole organism such as a laboratory animal—which allows assessment of effects across the entire biological system. A study using cell cultures is in vitro, meaning it happens outside a living organism in a controlled dish or tube, focusing on cellular or tissue-level responses without the complexity of an entire organism. This distinction is exactly what the statement captures: in vivo involves a living organism, while cell culture work falls under in vitro. The other ideas are not correct because in vivo studies can involve whole animals (not just artificial models), in vitro studies do not involve animals, and GLP applies to both in vivo and in vitro nonclinical studies.