Draize-Type Tests

All Draize-type tests evaluate corrosion and irritation by using albino rabbits as subjects (Table 3). The Federal Hazardous Substance Act (FHSA) adopted one modification as a standard procedure to this method (1997). 

Further description of the test see Chapters I.H (Peripheral Nervous System) and 1.0 (Ocular Toxicity Tests). 

The backs of 6 albino rabbits are clipped free of hair. Each material is tested on two 1-in square sites on the same animal one site is intact and one is abraded in such a way that the stratum comeum is open but no bleeding produced. Abrasion can be performed using the tip of a hypodermic needle drawn across the skin repeatedly or commercial instruments such as the 

Berkeley Scarifier as described by Haley et al. (1974). Materials are tested undiluted, and 0.5 ml liquid, or 0.5 g solid or semisolid material is applied. Each test site is covered with two layers of 1-in square surgical gauze secured in place with tape. The entire trunk of the animal is then wrapped with rubberized cloth or other occlusive impervious material to retard evaporation of the substances and hold the patches in one position. The wrappings are removed 24 h after application and the test sites are evaluated for erythema and edema using a prescribed scale. Evaluations of abraded and intact sites are recorded separately. Test sites are evaluated again 48 h later (72 h after application) using the same scale. 

The Draize test provides tremendous value in warning consumers, workers and manufacturers of potential dangers associated with specific chemicals so that appropriate precautions can be taken. Although vesiculation, ulceration, and severe eschar formations are not included in the Draize Scoring Scales, all Draize-type tests are used to evaluate corrosion as well as irritation. 

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The Draize method has generally erred on the side of safety in that it over predicts the severity of skin damage produced by chemicals, thus producing a safety factor for those exposed. Some investigators report repeatedly that the test is not sensitive enough to separate mild from moderate irritants. Although Draize-type tests will be replaced by in vitro assays some time in the future, we have no validated in vitro substitute at present. 

These are animal assays that evaluate the ability of chemicals to produce cumulative irritation. Many such tests have been described in literature, but only a few have been studied extensively enough to mention. Even those used more often are not as well standardized as Draize-type tests, and many variables have been introduced by multiple investigators. 

Irritation Tests in Animals Draize-Type Tests... 

Only a few in vivo dermal toxicity studies have been reported so far. Huczko and Lange [50] evaluated the potential of raw CNTs to induce skin irritation by conducting two routine dermatological tests (patch test on 40 volunteers with allergy susceptibilities and Draize rabbit eye test on four albino rabbits). Koyama etal. [51] showed the biological responses to four different types of carbon nanotubes (SWNTs, two types of MWNTs with different diameters, and cup-stacked carbon nanotubes) after their subcutaneous implantation in mice. Both tests [50, 51] showed no or poor irritation effects. However, the in vitro studies in epidermal cell lines exposed to CNTs, and also a more recent report on the toxic outcomes of topical exposure of mice to SWNTs [46], have raised concerns over these assessments. Clearly, this is an area requiring further scientific evaluation. 

Local tolerance assessments are usually incorporated into repeat-dose toxicity studies. Specific assessments include clinical observations (e.g.,Draize scoring) and macroscopic and microscopic evaluations of the injection site. These types of studies may also be used to test formulation changes during the course of clinical development. 

There are several types of irritancy testing protocols that are used to comply with federal and international safety regulations. The classic Draize test was developed in 1944 to measure acute primary irritation. The test compound is applied in an occluded fashion to a clipped area of abraded and intact skin of at least six albino rabbits and evaluated 24 hr and 72 hr after patch removal. The degree of erythema and edema, ranging from one to four, is recorded to reflect severity of the irritation. Because these tests are occluded, irritancy is potentiated due to hydration, which reduces the skin barrier. The Draize test may be modified to assess sensitization by preexposing animals to a sensitizing dose of the study chemical and then rechallenging the animals at a later date to illicit the immune-mediated response. 

The last type of acute test we will discuss is the (in)famous Draize test. This is an acute test that evaluates potential eye irritation, and was developed for the cosmetic industry to ensure that products used in eye makeup would not irritate the eyes. In this test, the chemical is placed directly on the cornea of the test animal using an eyedropper. The scientist then observes the signs and describes any lesions seen in the cornea, iris, or elsewhere in the eye and surrounding tissue. The test is considered cruel by many because the effects of the chemical often include pain and swelling of the eyes. However, this is one situation where in vitro tests would not provide similar information because ocular inflammation and other signs would not be reproduced in a beaker. 

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