The term is primarily applied in drug discovery, pharmacology, toxicology, biotechnology and medical research. If researchers give a potential medicine to an animal and observe how the body responds, for example, that is an in vivo study.
In vivo research is useful because a living body is much more complicated than a collection of cells in a laboratory. A substance introduced into the body can be absorbed, transported through the blood, changed by enzymes, processed by the liver and eventually removed through the kidneys or other routes. It can also interact with several tissues and biological systems at the same time. These processes can be difficult to reproduce fully outside a living organism.
What does in vivo mean?
In other words, ‘in vivo’ refers to experiments conducted on living organisms.
In the process of developing drugs, researchers first need to carry out in vitro experiments before moving on to in vivo tests. The process typically begins with testing using enzymes, isolated protein or cultured cells (in vitro) until they have demonstrated that the treatment produces the desired effect. If the experiment turns out to be successful, scientists can continue with in vivo experimentation.
The findings of a particular in vivo experiment can vary depending on its purpose. Scientists may wish to find out how effective the treatment is, how long the treatment remains in the body, or whether it does, in fact, lead to side effects.
The findings allow scientists to better understand how the compound behaves in conditions that resemble those found in a complex biological system.
In vivo vs in vitro
In vitro and in vivo denote two contrasting approaches to research.
In vitro studies are carried out outside a living organism. Most typically, the approach consists in working with cells, tissues, enzymes or any other biological materials either in isolated laboratory vessels or in specialised systems such as bioreactors.
In vivo studies involve work performed within a living organism.
For example, if a scientist exposes cultured cells to a candidate drug compound in vitro and assesses their reaction, the same approach can also be pursued in vivo in case the drug is administered to a living organism for testing the effects of the drug on a certain disease process.
Both practices have their advantages. In vitro studies provide researchers with an opportunity to look into a specific process under controlled conditions, whereas in vivo experiments incorporate the complexity of the whole organism, enabling scientists to learn unforeseen effects of the compound.
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Why are in vivo studies important?
A promising result in a laboratory dish does not always mean that a compound will work in a living organism. Once a substance enters the body, many things can happen to it.
For example, a medication may not enter circulation as intended. It may be degraded prior to reaching its destination, or it may be transported to preliminary tissues. A substance could affect another organ or body mechanism and cause an undesired impact that was not noticed during a previous laboratory test.
In vivo studies assist researchers in studying these issues. They are especially important for pharmacokinetics, which analyses what a body does to certain medicine, which includes absorption and distribution of a medication in an organism as well as its metabolism and excretion. Moreover, scientists conduct pharmacodynamics studies so that they are able to trace the way in which a drug influences a body on the basis of different doses applied.
Such data allow clarifying types of action for various substances before starting further processes of their development.
How are in vivo studies carried out?
The design of an in vivo study depends on the scientific question being investigated. Researchers may administer a test compound and then collect samples at different times. Blood, urine or tissue samples can be analysed to see how much of the compound is present or whether it has produced a particular biological response.
Other measurements may include changes in body weight, behaviour, physiological functions, disease-related symptoms or specific biomarkers.
The way a compound is administered can also affect the results. Depending on the study, it may be given orally, injected, inhaled or delivered through another suitable route.
Researchers need to consider several factors when designing these studies. The dose, timing, species, age, sex and general health of the model can all influence the results. A well-designed study therefore needs clear objectives and appropriate controls.
In vivo models in drug development
Animal models have been used extensively in biomedical and pharmaceutical research. Through their research, scientists can learn about the causes of diseases, look for possible treatments, and work on ways to be sure that drugs are safe for humans before they do research with people.
However, animals and people have different biological systems. What a particular drug does with an animal may be different from its effects on people. This is one of the reasons why the results of one study performed with animals need to be combined with the results of other types of research, rather than taken independently.
Scientists also bring together results obtained in laboratories, animal experiments, pharmacology, toxicology, and clinical studies when they want to gain more information about the treatment they are researching.
Using methods to eliminate or reduce the amount of animal testing is becoming more popular these days. Different technologies like organoids, organ-on-a-chip system, and different computer models are being developed to achieve this goal, though at the moment they are still not able to reproduce all functions performed by living beings.
What is an in vivo assay?
An in vivo assay refers to a procedure that is carried out in a living organism to assess a certain biological response.
For instance, scientists might carry out an in vivo assay in order to determine whether a candidate therapy leads to a decrease in inflammatory response, a change in physiological reaction, or an influence on disease progression.
Which specific parameters are measured depends on the study goals. Researchers may look for certain biomarkers, changes in tissues, physiological indicators, and other measurable results.
Due to the fact that many biological processes take place in a living organism, in vivo assays tend to be more complicated than laboratory tests. However, such complexity has its benefits when researchers want to understand the way the drug will behave in the organism rather than in one isolated system.
Why does in vivo matter?
In vivo studies help scientists understand what happens when a substance interacts with the whole living system. These studies can show the true difference between results in laboratories and the effects in a living organism, as well as help in the understanding of the activity, safety and behaviour of drugs.
The term is not complicated: ‘in vivo’ means ‘inside a living organism’. Its application in sciences is, however, very broad.
In vivo research can be used in combination with in vitro testing and other methods to give the researcher more information about how the compound or treatment works in biological conditions. This information may be useful in deciding what needs to be checked in the next stage of research.
Research Use Only. This glossary explains terminology used in published research. It is not medical advice and does not describe any product for human or animal use.