Medical articles for general audiences often use the terms “in vitro” and “in vivo” to describe studies. In vitro is Latin for “in glass.” In vivo is Latin for “within the living.”
This article will define both terms and discuss how they impact medical research.
In vitro is Latin for “in glass.” It describes medical procedures, tests, and experiments that researchers perform outside of a living organism. An in vitro study occurs in a controlled environment, such as a test tube or petri dish.
In vivo is Latin for “within the living.” It refers to tests, experiments, and procedures that researchers perform in or on a whole living organism, such as a person, laboratory animal, or plant.
Researchers use in vivo and in vitro methodologies to advance our knowledge of illness, disease, and the human body.
In scientific studies, researchers can test a hypothesis using one or both of these methods.
In vitro testing occurs in a laboratory and usually involves studying microorganisms or human or animal cells in culture. This methodology allows scientists to evaluate various biological phenomena in specific cells without the distractions and potential confounding variables present in whole organisms.
In vitro testing is a straightforward research methodology. Researchers can perform more detailed analyses and examine biological effects in a larger number of in vitro subjects than they would in animal or human trials.
However, although petri dishes and test tubes provide controlled environments for in vitro testing, they cannot replicate the conditions that occur inside a living organism.
As a result, it is necessary to interpret in vitro data with caution, as these results do not necessarily predict the reaction of an entire living being.
Some examples of in vitro testing include pharmaceutical testing and fertility treatments.
New drugs, also known as drug candidates, undergo in vitro testing before they enter clinical trials.
During an in vitro preclinical test, researchers will expose target cells to a novel drug and monitor its effects. In vitro testing is especially helpful for identifying whether or not a novel drug has any toxic or carcinogenic effects.
In a 2018 study, researchers in Italy used in vitro testing to monitor the toxic effects of molybdenum oxide nanoparticles, a promising new cancer treatment. Nanoparticles are small, or ultrafine, particles that are typically 1–100 nanometers in size.
The authors of one 2017 study identified personalized cancer treatment options using in vitro models.
In the study, the researchers collected cells from two uterine and two colon tumors. They analyzed these tumor cells using high throughput drug screening, which combines biology, robotics, and data processing to test thousands of different biological compounds on a single target cell.
The analysis identified effective drugs and drug combinations specific to each cell sample.
In vitro fertilization (IVF) is a type of fertility treatment where fertilization occurs in a laboratory, instead of within the body.
IVF involves extracting one or more eggs from an ovary and placing them in a petri dish with donated sperm. Fertilization usually occurs within 3–5 days.
A healthcare professional can then implant the resulting embryos into the uterus.
Despite positive preclinical results, around 30% of drug candidates fail human clinical trials due to causing adverse side effects. An additional 60% do not produce the desired effect.
In vivo testing, especially in clinical trials, is a vital aspect of medical research in general. In vivo studies provide valuable information regarding the effects of a particular substance or disease progression in a whole, living organism.
The main types of in vivo tests are animal studies and clinical trials.
Researchers use animal studies to uncover the mechanisms that underlie various disease processes and to assess the safety of emerging medical treatments.
Animal studies act as a kind of middle ground between in vitro experiments and human trials. Most animal studies use laboratory-bred mice or rats that are almost genetically identical. As a result, researchers can monitor various biological effects within complex organisms.
Testing genetically similar subjects in a laboratory environment offers a degree of control that does not exist in a clinical trial.
If a drug candidate appears both safe and effective in in vitro and animal studies, researchers will evaluate its effects in humans through clinical trials.
Researchers often compare the effects of new drugs against those of a placebo.
Many consider randomized controlled trials (RCTs) the gold standard for pharmaceutical testing. All RCTs must include randomization and control.
In randomization, the researchers randomly assign the participants to either the treatment or placebo group.
With control, the researchers compare the results from the participant who received the new drug or intervention with those from a participant in the control group. The participants in the control group get an alternative treatment, such as a placebo or an older form of the new drug.
Researchers may choose to “blind” their RCT by withholding information that could influence the participant involved in the experiment until the trial ends.
A blinded RCT might involve distributing the treatment and placebo in identical capsules so the participants cannot tell which treatment group they are in.
Blinding can also involve withholding information from members of the research team as well as the participants. This is known as double-blinding.
Blinding helps reduce bias or systematic errors that can jeopardize the design of a study and the validity of its results.
In vitro and in vivo studies provide valuable information for all stages of biomedical research.
Researchers often use in vitro methods for foundational investigations to examine drug interactions and disease processes at the cellular level.
In vivo studies expand on data from in vitro studies by monitoring biological responses in living organisms.