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In vitro and in vivo studies – understanding the terminology

 

There are many different types of research, some of which occur before interventions or medications are tested in clinical practice. Understanding the background of these preclinical investigations is important when considering the safety or efficacy of an intervention or drug. This article explores the differences between in vitro and in vivo studies and their relevance in clinical practice.

In vitro and in vivo studies – understanding the terminology
In vitro studies

To understand the effects of medication, dressings, or disease processes at a cellular level, preclinical trials are often undertaken in a laboratory setting. This involves testing outside the human body using microorganisms, human or animal cells in culture, or biological molecules (Dornell, 2023). This type of research is known as in vitro research and helps to increase knowledge of disease processes and functions of the human body at a cellular level (Eske, 2023; Uttekar, 2024).

The term in vitro translates as ‘under the glass’ and typically refers to experiments conducted in test tubes, petri dishes, or other controlled laboratory environments (Dornell, 2023). This method is used to cultivate viruses, bacteria, or fungi or to evaluate the effects of new drugs, dressings, or other products at a cellular level and to understand how cells may respond when exposed to certain circumstances or compounds (Dornell, 2023). Specific cells are usually targeted, making this technique valuable for research, preclinical trials, and scientific studies (Eske, 2023).

In vitro testing helps investigators to understand how a drug or intervention interacts with the body, allowing the development of safer and more effective treatments before they are introduced to the general population (Dornell, 2023).
Examples of in vitro testing:
  • Chemical analysis – e.g. Blood sampling
  • Microbiological studies – e.g. Using bacteria or fungi
  • Cytology – e.g. Examining tissue biopsies
(Polit and Hungler, 1997).
In vitro testing offers several advantages, including:
  • the ability to examine the effects on a specific target process without influences from potential confounding factors
  • it is easy and straightforward to undertake compared to other clinical studies such as in vivo research
  • large numbers of samples can be tested at one time
  • no live subjects are put at risk
  • they avoid or reduce the need to submit animal protocols and remove the added cost of ensuring animal welfare
  • they are cheaper to undertake than in vivo research
(Polli, 2008; Eske, 2023; Institute of Medicine (US) and National Research Council (US) Committee on the Framework for Evaluating the Safety of Dietary Supplements, 2025)
In vitro research is often the first step in generating hypotheses and identifying potential harmful effects on humans (Institute of Medicine (US) and National Research Council (US) Committee on the Framework for Evaluating the Safety of Dietary Supplements, 2025). However, it does not account for individual variations such as biological or physiological variables (Dornell, 2023; Institute of Medicine (US) and National Research Council (US) Committee on the Framework for Evaluating the Safety of Dietary Supplements, 2025). For example, when evaluating a drug that will be taken orally, in vitro testing cannot fully capture how compounds are metabolised or how they interact with complex biological processes such as ingestion, absorption, distribution, and excretion within the human body.

For this reason, in vitro research is often the first step in establishing a hypothesis, ahead of in vivo research being carried out.
Hypothesis

A hypothesis is a supposition or proposed explanation made based on limited evidence as a starting point for further investigation. Studies are carried out to test whether the assumptions made in the hypothesis are true or not, and the results of these studies inform the development of the research and further hypotheses.
In vivo research

To understand the broader effects of medications and interventions, in vivo studies are usually needed in addition to in vitro studies (Eske, 2023). In vivo is derived from the Latin ‘within the living’ (Dornell, 2023). These studies are performed on a whole living organism such as a human, a laboratory animal or a plant (Eske, 2023). This provides a deeper understanding of the effects of a drug, an intervention, or how a disease progresses within a living organism (Eske, 2023).

There are two types of in vivo studies:
Animal studies

Animal studies are sometimes used to evaluate the safety and efficacy of medications and tend to be used before a drug is given to humans (Dornell, 2023). They are usually conducted on laboratory-bred mice or rats and allow researchers to study different biological effects within a living organism (Eske, 2023). Animal studies are subject to strict protocols and regulations to ensure the welfare and minimise the suffering of the animals (Percie du Sert et al, 2020). Animal studies have been criticised because of potential limitations in translating results to humans, as physiological differences between species can affect outcomes (Akhtar, 2015).
 
Clinical trials
Once the safety and efficacy of an intervention has been established from in vitro and animal studies then trials can move on the human studies. Participants who choose to take place in trials are closely monitored to further evaluate the effect and safety of the intervention on the intended population (Dornell, 2023). Different types of clinical trials will be discussed in future articles in this series.
Disadvantages of in vivo research:
  • Expensive to undertake
  • Can take extensive periods of time to complete
  • Strict regulations and compliance standards must be adhered to.
Conclusion

In vitro and in vivo studies play a crucial role in all stages of biomedical research. Researchers commonly use in vitro methods for initial investigations, allowing them to study drug interactions and disease processes at the cellular level. In vivo studies build upon in vitro findings by observing biological responses within living organisms, providing a more comprehensive understanding of the effects of drugs, interventions or disease processes, and informing the development of future research.

References

Akhtar A (2015) The flaws and human harms of animal experimentation. Camb Q Healthc Ethics. 24(4):407-19. doi: 10.1017/S0963180115000079

Dornell J (2023) In Vivo and In Vitro: Definition, Pros and Cons. https://www.technologynetworks.com/drug-discovery/articles/in-vivo-vs-in-vitro-definition-pros-and-cons-350415 (accessed10 March 2025)

Eske J (2023) What is the difference between in vivo and in vitro? https://www.medicalnewstoday.com/articles/in-vivo-vs-in-vitro (accessed 10 March 2025)

Institute of Medicine (US) and National Research Council (US) Committee on the Framework for Evaluating the Safety of Dietary Supplements (2005) Categories of Scientific Evidence—In Vitro Data. In: Dietary Supplements: A Framework for Evaluating Safety. Washington (DC): National Academies Press (US), https://www.ncbi.nlm.nih.gov/books/NBK216047/ (accessed10 March 2025)

Percie du Sert N, Hurst V, Ahluwalia A et al (2020) The ARRIVE guidelines 2.0: updated guidelines for reporting animal research. PLoS Biol. 18(7):e3000410. doi: 10.1371/journal.pbio.3000410

Polit D, Hungler B (1997) Essentials of nursing research: methods, appraisal and utilization. 4th edn. Philadelphia: Lippincott-Raven; 280-282

Polli JE (2008) In vitro studies are sometimes better than conventional human pharmacokinetic in vivo studies in assessing bioequivalence of immediate-release solid oral dosage forms. AAPS J. 10(2):289-99. doi: 10.1208/s12248-008-9027-6

Uttekar PS (2024) Why is in vivo better than in vitro? https://www.medicinenet.com/why_is_in_vivo_better_than_in_vitro/article.htm (accessed 10 March 2025)