Single-application patch tests

At the very least, to support limited topical exposure, for example, single application patch test in the human, genotoxicity data are required (and a favourable judgement on the sensitization and corrosive potential of the material). The following types of study may be performed using human volunteers. 

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. 

True IgE-mediated anaphylactic reactions to LAs are extremely rare [11-13]. Only single cases have been reported in the literature with positive prick tests [ 14,15]. A case of a positive open patch test in a patient suffering from contact urticaria after topical application of lidocaine, pilocaine mixture (Emla cream) might represent a true IgE-mediated allergy [16]. The maj ority of immediate-type reactions are non-immune in nature. 

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. ... 

After 8 daily applications we observed a clear sensitization in some guinea pigs, demonstrated by the patch test on the flank (out of 10 tests, 5 were positive). After 20 to 40 applications on a single nipple, the patch tests on the flanks are positive in almost all of the guinea pigs. Therefore, a general sensitization occurs even though the multiple applications are performed on a very small surface and with a primary non-toxic solution of DNCB (Table 1). 

We have seen elsewhere that if one applies daily a solution of 0.1% DNCB in acetone to a single nipple of a nonsensitized guinea pig (5, 8, 20 applications), acanthosis increases regularly on this nipple at the same time as the eczematous lesions are developing. Some eczematous lesions also appear and progressively grow in intensity on the flank and the other nipple, after a patch test (0.1% in acetone) (Table 5). 

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. 

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. 

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