Repeat application patch tests

Objective irritation is defined as nonimmunologically mediated, localized inflammation of the skin, usually resulting from contact with a substance that chemically damages the skin.2,9 The exact mechanism is unknown, and it is likely that both endogenous and exogenous factors are involved. In vivo predictive testing in animals (e.g., modified Draize test, repeated application patch tests,... 

Repeat application patch tests - diluted materials are applied to the same site each day for 15-21 days... 

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. 

Repeated-application patch tests on intact skin fail to predict some adverse reactions due to repeated application of materials to damaged skin (i.e., acne, shaved underarms, or sensitive areas such as the face). 

Repeat application patch tests in which diluted materials are applied to the same site each day for 15-21 days have been reported using several species (the guinea pig or rabbit being most commonly used) (Phillips et al. 1972). Because the degree of occlusion is an important determinant of percutaneous penetration, the choice of covering materials may determine the sensitivity of a given test (Mag-nusson and Hersle 1965). A reference material of... 

There are several acceptable ways to evaluate DTH responses in nonclinical species. Of these, the most common are the guinea pig assays used to assess contact sensitization. Both the Magnusson and Kligman model (guinea pig maximization test) and the Buehler model measure the elicitation phase of the hypersensitivity response, though the tests vary in their methods of chemical application and utilization of adjuvants. Most recently, the local lymph node assay has been accepted as a stand alone test for chemical hypersensitivity. This assay is conducted in mice and measures the induction phase of sensitization. In humans, the most common methods to assess delayed hypersensitivity are the patch test (contact sensitivity for diagnostic purposes) and the human repeat insult patch test (contact sensitivity for predictive purposes). Additionally, intradermal... 

Many industries regularly conduct repeat insult patch tests on human volunteers to evaluate topical irritancy. Groups of human volunteers are patched with test substance. One to five concentrations can be tested simultaneously, a wide enough range to yield results relevant to the usage. Cumulative skin irritancy is measured by applying patch applications each day for 3 weeks. Skin irritation is usually assessed visually, but blood flow and skin temperature can be measured objectively by laser Doppler flowmetry, ultrasound Doppler, heat flow disk measurement, sensitive thermocouple devices, or noncontact infrared radiative techniques. In these tests, dose-response curves can be obtained. Skin thickness can be measured with calipers as a measure of edema formation. 

Human volunteers are also used in many industries in tests for allergic sensitization by cosmetic substances and formulations. The repeat insult patch test includes an induction phase (repeat applications during 3 weeks) and a 2 week rest period (incubation phase), followed by a challenge to see if sensitization has occurred. A pilot study of 20 human volunteers can be followed by more extensive testing (80-100 subjects). Positive results at more than the 10% level in the human volunteers would suggest a major problem with the formulation. User tests with the sensitized individuals and nonreactive matched control subjects can often determine the importance... 

Organophosphate Ester Hydraulic Fluids. Repeated application of a patch treated with 0.2 pL of Skydrol 500B-4 for 5 weeks (3 times/week) resulted in mild cumulative erythema confined to the contact site in 14 of 53 human test subjects, beginning with the third dose during the first week. No evidence of immediate primary dermal irritation was observed (Monsanto 1980). 

NMP produced no skin irritation with patch testing for 24 hours in 50 volunteers. A few mild transient reactions were noted after repeated application. There was no evidence of contact sensitization. 

Repeat Animal Patch (RAP) test - compares irritation potential of surfactants. Solutions were applied to the clipped back of immobilized albino mice with a saturated cotton-tipped applicator. The test site was covered with a rubber dam to prevent evaporation. This process was repeated seven times at intervals of 10 min. The skins were evaluated microscopically for epidermal erosion. 

A patient with a contact allergic reaction to a topical antimycotic drug formulation that contained benzoyl alcohol had positive patch tests on day 4 and a positive repeated open application test to benzoyl alcohol 5% in petroleum jelly (3). 

Patch tests in patients with anogenital eczema should include the standard series cinchocaine HCl, propolis, bufexamac, and other ingredients of topical formulations according to the patient s history. In cases of doubt, the repeated open application test (ROAT) is recommended. Patients should be advised to apply the suspected product three times a day for 3 days to an area of healthy skin on measuring 5 cm x 5 cm the flexural site of the forearm (35). 

Brown and Kaplan presented a more complex solution of phenol (at varying concentrations between 60% and 95%) mixed with saponified cresol in oil at concentrations of up to 10%. The application technique included a patch test behind the ear. This test made it possible to assess the necrotic effect of the solution on the patient. If the necrosis was too severe, the test was repeated with increasing concentrations of oil until the right solution for the patient was found. They recommended applying the solution area by area, leaving 2 hours between applications. The peel took 2 days to complete. 

Flyvholm M-A, Hall BM, Agner T, et al. 1997. Threshold for occluded formaldehyde patch test in formaldehyde-sensitive patients Relationship to repeated open application test with a product containing formaldehyde releaser. Contact Dermatitis 36 26-33. 

Application of a test patch should be discontinued at a site if predefined serious reactions occur at the site of repeated applications. Application at a different site may subsequently be initiated. 

The types of tests used to assess skin irritation potential of ingredients or products are many and varied. Tests on animals of different species are used to assess safety and are usually blunt tools. Rabbits, guinea pigs, and humans are frequently used species. Fluman in vivo tests of products or solutions of ingredients applied under patches or in plastic or glass chambers have been used. Arm or hand immersion or repeat applications to sensitive areas (e.g., the inside of the forearms or the cheeks) are also common test sites. 

Patch testing and/or photopatch testing, which are performed in the usual way. There are no specific techniques that are recommended for airborne dermatitis. The methodology also includes additional procedures, such as open tests, repeated open-application tests and, eventually, use tests. 

Perform additional testing procedures with the suspected allergen(s), products brought by the patient presumably containing the suspected dlergen and product s extracts Perform patch test with serial dilution Perform provocative use test Perform repeated open-application test... 

Use tests and open tests are sometimes used as synonyms. The original (provocative) use (or usage) tests were intended to mimic the actual use situation (repeated open applications) of a formulated product, such as an oil, shampoo or a topical medicament. A positive result supported the suspicion that the product had caused the patient s dermatitis. Nowadays, these tests are increasingly used to evaluate the clinical significance of one or more ingredients of a formulated product previously found reactive by ordinary patch testing. The concentration of the particular ingredient can be so low that one may wonder whether the positive patch-test reaction can explain the patient s dermatitis. 

Clinical relevance of a positive patch-test reaction may exist for at least 55-65% of positive results. Strongly positive patch test reactions (2+ or 3+) are more likely to be associated with a positive fragrance history than a weak or doubtful reaction (Frosch et al. 1995b). A positive ROAT (repeated open application test, twice daily application on the antecubital fossa for a maximum of two weeks) (Johansen et al. 1996) with fragrance ingredients makes relevance of the reaction more likely. 

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). 

Information regarding test concentrations and vehicles are rarely available - for the examining dermatologist, the testing is a question of trial and error. If a positive reaction is obtained, it is crucial to carry out serial dilution tests and to test a sufficient number of controls (>25). So far, provocative use tests, such as the repeated open application test (ROAT), do not seem to have been used to clarify the relevance of a positive patch-test reaction to a solvent. 

Such tests are suitable for identifying highly irritant material, not for comparing irritancy potential of different products. Repeated open application tests are also frequently used to verify the clinical significance of allergic patch test reactions [55]. 

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