The maximization test for skin sensitization potential--updating the standard protocol and validation of a modified protocol

Guinea pigs in hypersensitivity testing

The aim of the present paper is to mention steps of development of predictive guinea pig animal models for contact sensitization evaluation in parallel with the development of understanding the mechanism of contact sensitization. The guinea pigs methods are reviewed and the presently accepted methods (Buehler test, Maximization test) are discussed in details. Influences on the outcome of guinea pig sensitization assays are mentioned too. The predictability of the guinea pig methods is compared with predictive methods in mice, with human tests (human repeated insult patch test, HRIPT) and epidemiological data. In the last part, a testing strategy and steps for risk assessment of contact sensitizing potential is proposed.

The value and limitations of rechallenge in the guinea pig maximization test

The guinea pig maximization test (GPMT) has played a primary rôle in the evaluation of potential skin contact sensitizers for 25 years. In the OECD Guideline 406 from 1993, it is specifically suggested that equivocal results from the initial challenge in the GPMT should be evaluated further with a repeated challenge. However, there exist few published rechallenge data and the guideline does not describe how rechallenge data should be interpreted. In this paper, we have used examples from published results to illustrate both the positive value and the limitations of repeated challenges, including cross challenge. Testing with modified concentrations may also help to indicate whether or not the response is allergic in nature, particularly where there has been a low level of skin reaction observed in shamtreated controls, or where a low level of skin reaction is the dominant response in the test animals. In conclusion, the data presented demonstrate that, as a tool for the investigation of skin sensitizing potential, the GPMT can benefit from an experienced scientific evaluation of rechallenge data, but that this information should not be treated in a mechanistic fashion.

Testing for skin sensitization according to the notification procedure for new chemicals: the Magnusson and Kligman test

The notification procedure for new chemicals in the European Union (called the Chemicals Act in Germany) requires a skin sensitization test when the amount of a new chemical produced exceeds 100 kg/year. The preferred test is that of Magnusson and Kligman; more than 90% of the tests submitted are performed with it. Though the Magnusson and Kligman test is described in the literature, and in the test guidelines of the European Union and of the OECD, discrepancies do occur in the performance of the test between test laboratories. In this paper, recommendations are given for standardized performance of the Magnusson and Kligman test.

The safety assessment of over-the-counter (OTC) products

In recent years many compounds have become available as Over-The-Counter (OTC) medicine, for self-medication, which were originally marketed as prescription medicines only. This has been coupled with changes in the consumers' behaviour to self treatment and the governments commitment to restrict rising health costs. The safety and safe use of OTC products are important considerations for their wide distribution which is paralleled by diminishing medical supervision. OTC products were generally registered when toxicological requirements differed from the stringent guidelines of today, and their safety assessment thus often involves ongoing evaluation as new data become available. For this, human data must also be integrated for these assessments. However, in some areas, such as mutagenicity and carcinogenicity testing, human data are hardly obtainable and testing in animals or cells, is ultimately the only reliable source for extrapolation to man. Routine toxicological methods have mainly been developed for the assessment of new pharmaceutical entities and often provide 'yes/no' answers only. Data of such tests are, therefore, not directly applicable to the safety assessment of OTC products. Additional information on the kinetics in animal and man are indispensable for such extrapolation. On the other hand, modifications of original test protocols for the assessment of new formulations are indispensable. It was the aim of this workshop to discuss general approaches of safety assessments within the important new area of OTC products, as well as to present specific cases of recently arisen safety issues.

The local lymph node assay: developments and applications

The murine local lymph node assay is a predictive test method for the identification of contact allergens in which sensitizing activity is measured as a function of induced proliferative responses in lymph nodes draining the site of application. In this article the development and validation of the assay are described and comparisons with guinea pig predictive test methods discussed. In addition we examine the advantages and limitations of the method and consider new opportunities and applications of the assay in the context of the toxicological evaluation of sensitizing potential.

Guinea-pig contact sensitization assays

After reviewing general aspects and the historical development of predictive animal skin sensitization tests, the recommended tests of the OECD and EC are discussed. Background information is given on the changes which occurred in the last 2 years. From the many factors known to influence induction and challenge of contact allergy in animals, the discussion is focused on the choice of induction concentration and the vehicle. The difference of general screening strategies in Europe and the USA is presented and discussed. The paper closes with a discussion on the importance of inhouse validation of the methods used for proper prediction of the sensitizing potential of chemicals and with remarks on predictive in vitro tests.