Ethics of Research involving animals
Animal use in toxicity testing (Chapter 9)
10.23 Tests involving animals play an important role in the safety assessment of compounds such as medicines, household chemicals, agrochemicals and industrial chemicals when brought into contact with humans, animals or the environment. Chemicals are assessed for their potential to cause irritation, physiological reactions, cancers, developmental complications for foetuses in utero, and effects on fertility. Sixteen percent of the total number of procedures using animals in 2003 in the UK were conducted for the purpose of ‘toxicology or safety evaluation’. Specified doses and exposures of the chemicals are given to animals, from which information regarding safe human dose and exposure levels is then extrapolated.
10.24 Rats and mice are most commonly used in toxicology (74 percent of procedures). Other tests involve non-rodent species such as fish, rabbits, chickens, dogs and primates. Tests range from one single high dose to long-term exposure to a particular chemical, in order to observe the effects seen when a product is used (or misused) in different situations. The tests are designed to mimic the possible routes of exposure that humans might be subjected to, such as through the mouth, skin, eyes or airways. The information produced is used mainly to ascribe chemicals to bands of acute toxic effects, which restricts how they may be used. Regulatory requirements demand that the studies are conducted in a way that minimises the numbers of animals used and which reduces pain and distress as far as possible (paragraphs 9.4 and 13.17).
10.25 Toxicity testing has a range of welfare implications for test animals, some of which can be severe. These effects are minimised by the ‘build-up’ approach in which severe reactions can be detected at an early stage (acute toxicity followed by chronic toxicity, paragraph 9.14). More recently alternative methods have been developed which, when utilised during the early stages of testing, may prevent very toxic substances from being administered to animals. For example, studies that evaluate irritant potential to the skin or eye are preceded by tests that use in vitro human or animal tissue to identify chemicals with the potential to cause severe irritation or corrosion. These tests are termed ‘nonanimal pre-screens’. However, it is an intrinsic part of most toxicity tests to cause some form of harm to animals.
10.26 A full complement of toxicity tests can entail the use of between 1,500 and 3,000 animals, although not all of these will suffer the most harmful consequences of the testing. The adverse effects range from minor changes such as reduced weight gain to severe effects including loss of organ function, leading to death (paragraphs 9.32-9.37). Certain methods of reduction and refinement are relevant to toxicology, but progress has been difficult (paragraphs 9.3-9.4).