What Does In Vivo and In Vitro Mean?

In Vivo vs In Vitro - Definition, Similarities and Differences

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What are the differences between in vivo and in vitro medical studies?. Istockphoto.com/Stock Photo©AlexRaths

What is the difference between in vitro and in vivo medical studies, and what is the definition and importance of each of these?

Definition: In Vivo

The term in vivo refers to a medical test, experiment or procedure that is done on a living organism, such as a laboratory animal or human.

Definition: In Vitro

A study done in vitro, in contrast, looks at how a drug or procedure responds in the confines of a test tube or laboratory dish.

Differences Between In Vivo and In Vitro in Clinical Trials

Clinical trials or medical studies may be performed either in vivo or in vitro.  They are similar in that they are both done in order to make advances in our knowledge and treatment of illness and disease.  There are also many important differences.

In Vitro Medical Studies

Medical studies looking at a particular substance are often first performed in vitro -- either in a test tube or laboratory dish. With cancer, these dishes may contain lung cancer cells that have been grown outside of the body or a number of different mediums.

Studies are usually done in vitro for ethical reasons. In vitro studies allow a substance to be studied more safely, as human beings or animals are not subjected to the possible side effects of a new drug. This allows researchers to learn as much as possible about a drug before exposing humans.

In vitro studies are important in that they allow more rapid development of new treatments -- many drugs can be studied at one time and only those that appear to be efficacious go on to human studies.

In Vitro Clinical Trials

In contrast, in vivo studies are needed to see how the body as a whole will respond to a particular substance. In some cases in vitro studies of a drug will be promising, but subsequent in vivo studies fail to show any efficacy (or, on the other hand, find a drug to be unsafe) when used within the multiple metabolic processes that are continually taking place in the body.

An example of how in vivo studies are needed to evaluate drugs is with respect to drug absorption in the body.  A new drug may appear to work in a dish, but not in the lab. It could be that the drug is not absorbed when it passes through the stomach, so it has little effects on humans. In other cases, it could be that a drug is broken down by the body through any number of reactions that occur continuously, and therefore, the drug would not be effective when used directly in humans.

In Vivo vs In Vitro Studies

When you look at studies done to evaluate cancer treatments - or any other treatments - checking to see which kind of study it is (in vivo vs in vitro) is an important first step. In vitro studies are extremely important and lay the groundwork for further research, but many of these studies declare findings that are interesting - but will not affect you as an individual for quite some time to come. In contrast, in vivo studies are looking at the actual effect on an organism - whether a laboratory animal or a human.

It may be some time - if the study is an animal study - until the drug or procedure is evaluated in humans, but it is a step closer to being used in real life.

Examples: New chemotherapy drugs for lung cancer are usually studied in vitro before they are studied in vivo in clinical trials on humans.

Sources:

Emami, J. In vitro – in vivo correlation: from theory to applications. Journal of Pharmacy and Pharmacological Sciences. 2006. 9(2):169-89.

FDA. Drug Interaction Studies: Study Design, Data Analysis, Implications for Dosing and Labeling Recommendations. February 2012. http://www.fda.gov/downloads/drugs/guidancecomplianceregulatoryinformation/guidances/ucm292362.pdf

Killkenny, C. et al. Animal research: Reporting in vivo experiments: The ARRIVE guidelines. British Journal of Pharmacology. 2010. 160(7):1577-179.

MacGowan, A., Rogers, C., and K. Bowker. In Vitro Models, In Vivo Models, and Pharmocokinetics: What Can We Learn form In Vitro Models? Clinical Infectious Disease. 2001. 3(Suppl 3):S214-S220

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