Updating the skin sensitization in vitro data assessment paradigm in 2009.

Approaches to the interpretation of guinea pig skin sensitization data for both hazard identification and potency assessment have been understood for many years. More recently, the local lymph node assay has to a large extent replaced the earlier guinea pig assays, not least because it provides a more clearly defined and transparent means of identifying hazard, and the ability to measure relative skin sensitization potency. However, beginning in 2009 there will be considerable pressure replace all in vivo assays for skin sensitization with alternative approaches that do not require the use of animals (in vitro and/or in silico methods). As there is a common view that multiple assays will be needed to achieve complete replacement of the in vivo tests, a strategy for the integration of the available data will be required. There has been at least one previous attempt to develop a framework that would provide for integration of relevant information from different sources to reach informed decisions about skin sensitization potential and potency. It is timely now, in the light of recent developments and initiatives, to revisit this paradigm with a view to developing recommendations for modification and refinement. In addition to this, the need for performance standards and an agreed 'gold standard' dataset against which to validate both alternatives and new prediction models is discussed.