Cytotoxic Actions and Precautions

Cytotoxic refers to a substance or process which results in cell damage or cell death. The prefix "cyto" refers to cell and "toxic" to poison. The term is often used to describe chemotherapy drugs that kill cancer cells, but it may also be used to describe toxins, such as venom. Within our own immune systems, we have cells that are considered cytotoxic, such as the T cells that kill bacteria, viruses, and cancer cells. The label "cytotoxic" is important for medical professionals who will be handling cytotoxic medications or other substances that can cause cell death, and specific precautions are necessary for safety. Cytotoxicity testing is important in ensuring safety ranging from environmental exposures to medical devices.

Hand in latex glove holding IV system containing cytotoxic chemotherapy

Cytotoxic Drugs

Most of the time the term "cytotoxic" refers to the effect that a chemotherapy drug has on cancer cells. In this sense, a cytotoxic agent may be differentiated from one that is cytostatic. A cytostatic medication would, in contrast, inhibit cell division and growth but would not result in cell death directly.

Cytotoxic drugs work by interrupting cells at particular places in the growth cycle. They are most likely to affect cells that are growing rapidly, for example, cancer cells, hair follicles, bone marrow, and cells lining the stomach and intestines. The reason that most chemotherapy regimens include a combination of drugs (combination chemotherapy), and that most chemotherapy cycles are repeated, is because cells are in various places in the division process.

Not all drugs used to treat cancer are cytotoxic. Chemotherapy drugs are designed to kill all rapidly growing cells, including normal cells in the body that divide rapidly. Some of the newer types of cancer drugs, such as targeted therapies and immunotherapies, are not considered cytotoxic. These drugs work either to interfere with a particular pathway in the growth of cancer cells, or to stimulate or use the immune system in some way to fight cancer. Some immunotherapies, such as CAR T, may be considered cytotoxic in a way, as they take advantage of the cytotoxic actions of the body's own cytotoxic T cells.

Cytotoxic Agents in Humans or Animals

There are other cytotoxic substances used for a wide array of functions. As with cytotoxic chemotherapy drugs, this simply means that they kill cells.

Cytotoxic T cells

Cytotoxic agents are not just created to destroy cancers and control diseases. Our bodies also manufacture cytotoxic T-cells (cytotoxic T lymphocytes). Cytotoxic T cells (CD8+ cells and natural killer lymphocytes) are part of the immune system, which searches for, finds and destroys cells infected by viruses as well as cancer cells.

One of the most rapidly advancing areas of cancer research is now focusing on harnessing and stimulating our own cytotoxic cells to fight cancer in our bodies. These treatments work in a number of different ways; some by allowing the T cells to "see" cancer cells that were previously hidden, others by harvesting and multiplying these cells, and more.

Cytotoxic Venom

Humans are not alone in their use of cytotoxic T cells. Some venoms, such as those emitted by vipers, cobras, and violin spiders, are also cytotoxic.

Mechanism of Action

Cytotoxic agents can kill cells in several ways. They may harm the cell so that its cell membrane is weakened and the cell explodes (lysis) or they may interfere with cell division so the cell stops growing and dividing.

The terminology can be very confusing when looking at drugs or other substances that damage cells or DNA in cells.

Cytotoxic vs Genotoxic

There is much confusion between the terms cytotoxic and genotoxic. The term cytotoxic refers to the ability of a substance to cause damage to cells. The term genotoxic refers to the ability of a substance to directly damage DNA in cells. When DNA is damaged, it may or may not die. In fact, the persistence of cells harboring damaged DNA (mutations) that are not repaired underlies the development of cancer. Cancer often arises following a series of mutations in both oncogenes (genes that code for proteins that drive the growth of cells) and tumor suppressor genes (genes that code for proteins that repair damaged DNA or cause a cell to die if the DNA cannot be repaired). BRCA genes are examples of tumor suppressor genes.


A few other definitions are important to explain when talking about cytotoxicity. The term carcinogenic refers to a cytotoxic substance that has the ability to cause DNA damage that could ultimately lead to the development of cancer. In contrast, the term mutagenic refers to cytotoxic substances that could potentially instead damage the chromosomes or genes in a fetus.

This is why it is extremely important for people to practice caution when they are handling cytotoxic drugs and substances.

Dangers of Cytotoxic Drugs and Agents

Cytotoxic drugs can kill cancer cells but they can also damage normal, healthy cells as is evidenced by the side effects of most chemotherapy drugs.

Cytotoxic Precautions

For those who work with cytotoxic medications or other substances, precautions are recommended specifically to avoid carcinogenicity and mutagenicity. The specific precautions will vary considerably based on the route of possible exposure but may include:

  • Gloves, with cuffs tucked under the gloves
  • Long sleeve clothing
  • Disposable gowns
  • Safety glasses
  • Respiratory protection

With some cancer treatments, patients may be given cytotoxic precautions when returning home. These include measures to protect other family members who could inadvertently be exposed to body fluids containing cytotoxic chemicals.

Cytotoxicity Testing

Cytotoxicity testing is used in the development of many products ranging from drugs to cosmetics. Plant products (that will be used for extracts, etc.) are testing for toxicity. A term called the "selectivity index" describes the ratio between potential biological activity in a plant specimen relative to its potential cytotoxicity.

A Word From Verywell

The term "cytotoxic" can be frightening, especially if you see the label on something that will be injected into your body. But our own bodies make substances that are cytotoxic as well. It's important to understand how these substances, work, however, to protect yourself in the environment around us.

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  1. Andersen MH, Schrama D, Thor straten P, Becker JC. Cytotoxic T cells. J Invest Dermatol. 2006;126(1):32-41. doi:10.1038/sj.jid.5700001

  2. Riss TL, Moravec RA, Niles AL. Cytotoxicity testing: measuring viable cells, dead cells, and detecting mechanism of cell death. Methods Mol Biol. 2011;740:103-14. doi:10.1007/978-1-61779-108-6_12

  3. Bai J, Li Y, Zhang G. Cell cycle regulation and anticancer drug discoveryCancer Biol Med. 2017;14(4):348–362. doi:10.20892/j.issn.2095-3941.2017.0033

  4. Papaioannou NE, Beniata OV, Vitsos P, Tsitsilonis O, Samara P. Harnessing the immune system to improve cancer therapyAnn Transl Med. 2016;4(14):261. doi:10.21037/atm.2016.04.01

  5. Bracci L, Schiavoni G, Sistigu A, Belardelli F. Immune-based mechanisms of cytotoxic chemotherapy: implications for the design of novel and rationale-based combined treatments against cancerCell Death Differ. 2014;21(1):15–25. doi:10.1038/cdd.2013.67

  6. Casey SC, Vaccari M, Al-Mulla F, et al. The effect of environmental chemicals on the tumor microenvironmentCarcinogenesis. 2015;36 Suppl 1(Suppl 1):S160–S183. doi:10.1093/carcin/bgv035

  7. Szikriszt B, Póti Á, Pipek O, et al. A comprehensive survey of the mutagenic impact of common cancer cytotoxicsGenome Biol. 2016;17:99. doi:10.1186/s13059-016-0963-7

  8. Meade E. Avoiding accidental exposure to intravenous cytotoxic drugs. Br J Nurs. 2014;23(16):S34, S36-9. doi:10.12968/bjon.2014.23.Sup16.S34

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