Single-Application Irritation Patch Tests

Many forms of patch tests exist. Duration of patch exposure has varied between 1 and 72 h. The singleapplication patch procedure outlined by the NAS (1977) incorporates important aspects of assays used by many investigators. The procedure is similar to FHSA tests in rabbits. 

Commercial patches, chambers, gauze squares, or cotton bandage material, such as Webril, applied to either 

Responses are evaluated 30 min to 1 h after patch removal (to allow hydration and pressure effects to subside), and again 24 h after the patch is removed. Persistent reactions may be evaluated for 3 to 4 days. The Draize scales can be used to evaluate erythema and edema however, the integrated scales ranging from 4 to 16 points are preferred. Such integrated scales are able to score popular, vesicular or bullous responses in addition to erythema/edema evaluation. Up to 10 materials can be tested simultaneously on each subject. The position that the materials are placed on the skin (i.e., upper right back, lower left back, etc.) should be systematically varied within each study since skin reactivity varies by body region. 

The method has been used and modified by many authors, e.g. Wooding and Updyke (1967) Griffith et al. (1969). Regulatory agencies do not routinely require testing in men, however, human tests are preferred to animal tests in some cases secondary to uncertainties of interspecies extrapolation. 

It is possible to conduct predictive irritation assays in man as only a small area of the skin needs to be tested (provided that systemic toxicity is low and informed consent is obtained). Patch test responses generally heal rapidly, within a week or so. More severe reactions should be evaluated periodically over a longer period to determine how the inflammatory response is resolved. Some subjects may develop changes in pigmentation level at the test site following severe responses. It 

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Single applications of 1.0 ml of 1% CS solution were administered to the clipped backs of rabbits.29 They developed mild to moderate erythema chat cleared in 3 d. Monkeys showed no signs of irritation. A 5-d test of the 1% solution caused only moderate erythema that cleared in 8 d. A 0.2-ml application caused only moderate irritation in the rabbits. In monkeys, l-ml and 0.2-ml applications caused no irritation. Patch tests on rabbits and monkeys with similar doses caused somewhat more skin irritation, but generally the lesions were reversible no systemic toxicity was demonstrated. ... 

The potential of Ecoflex (powder) to cause acute dermal irritation or corrosion was assessed by a single topical application of the test substance to the intact skin of rabbits according to OECD guideline 404. After removal of the patch, the application area was washed off and cutaneous reactions were assessed for 72 h. No cutaneous reactions were observed. Hence, Ecoflex (powder) is not irritating to skin. 

PURPOSE AND RATIONALE Inflammation produced late in the induction phase of sensitization tests without positive responses at challenge is cumulative irritation. The HRIPT for skin allergy was modified to evaluate skin irritation. As with single-application patch tests, many investigators developed their own version of the repeat application patch test. 

Patch testing with serial dilution of nickel sulfate is sometimes used to gain more information on the degree of sensitivity and to discriminate between allergic reactions and irritant ones (Andersen et al. 1993 Wahlberg 1995). Open tests to study the concentration threshold have been carried out with nickel sulfate or chloride as single or repeated applications (Menne and Calvin 1993 Allenby and Basketter 1994). Intracutaneous testing with nickel sulfate is used at some centres (Moller 1989). 

In this test, three rabbits are used to assess the irritancy potential following a single 4-h semi-occluded application, to intact rabbit skin, of 0.5 mL or 0.5 g of test material. The skin is observed 30-69 min and approximately 24, 48 and 72 h after patch removal. If irritation is persistent, additional observations can be carried out on days 7 and 14. 

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