Processes or experiments conducted within living organisms
Explanation
In vivo, meaning “within the living,” refers to studies performed on whole, living organisms such as humans, animals or plants. In vivo experiments preserve the complex interactions among organs, tissues, immune responses, metabolism, hormones and nervous systems that cannot be replicated in cell culture. They are essential for understanding disease mechanisms, evaluating pharmacokinetics, pharmacodynamics and toxicity, and assessing efficacy of therapeutic interventions. Animal models, ranging from rodents and zebrafish to non‑human primates, are commonly used to simulate human physiology and disease. In vivo research includes observational studies, controlled laboratory experiments and clinical trials in humans. Techniques such as in vivo imaging (MRI, PET, fluorescence), electrophysiology and telemetry enable measurement of biological processes in real time. Compared with in vitro approaches, in vivo studies provide more accurate predictions of clinical outcomes but involve greater ethical considerations, higher cost and biological variability. Regulatory frameworks require that new drugs and vaccines demonstrate safety and efficacy in appropriate in vivo models before they progress to human trials.
Examples and applications
Preclinical testing of pharmaceuticals typically begins with in vivo toxicology studies in rodents to determine safe dosing. Vaccine candidates are evaluated by immunizing animals and challenging them with pathogens to measure protection. In vivo electrophysiological recordings in mice elucidate neuronal circuits underlying behavior. Xenograft models involve implanting human tumors into immunodeficient mice to study cancer growth and test chemotherapies. Clinical trials represent in vivo experiments in human volunteers and patients to evaluate new drugs, medical devices or surgical techniques. In vivo imaging technologies allow researchers to track stem cell engraftment, monitor tumor metabolism or visualize infection progression without sacrificing the organism.
In vivo studies provide crucial insight into how biological systems function in their natural context and guide the translation of basic research into safe and effective therapies.
Related Terms: In vitro, Animal model, Clinical trial, Pharmacokinetics, Ex vivo