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The Corrositex assay can be used to predict the potential of a substance to cause skin corrosion.

The method is based on the amount of time needed for a chemical to break through a biobarrier membrane and interact with an underlying chemical detection system.

The approach has received regulatory approval as a replacement of in vivo skin corrosivity tests for specific classes of chemicals (namely acids, bases and certain derivatives).

The results of the validation study, the ESAC statement and our recommendation will be soon available on TSAR, the Tracking System for Alternative methods towards Regulatory acceptance.

Skin corrosion

[collapsed]In most cases, skin corrosion refers to full thickness destruction of skin tissue by a chemical, and in the case of Corrositex assay this is the most appropriate description of the end-point used.

Skin corrosion can also refer to any irreversible alterations of skin tissue that is chemically-induced. Skin irritation, in contrast, refers mainly to changes in skin tissue that are reversible.

Skin corrosion potential is considered important for establishing safe handling practices, packaging and the transport of chemicals.[/collapse]

Corrositex

[collapsed]The Corrositex method was originally established to predict the skin corrosivity potential of chemicals and to rank them according to their degree of corrosive effect.

The assay is based on the determination of the time needed for a test material to pass through a biobarrier membrane. The membrane is a reconstituted collagen matrix with physical properties that are similar to rat skin.

The end-point is the time required to cause a colour change in an underlying 'chemical detection system'. The colour change is visually scored and therefore a subjective measurement (i.e. there is a potential variation in measurement outcomes due to operator variability).

The method was commercially developed and is considered to be a standardised, quantitative in vitro test for skin corrosivity that is useful in evaluating certain chemical classes.[/collapse]

Animal testing replacement

[collapsed]The test method has received regulatory approval as a replacement of the Draize rabbit skin test. However, limitations do apply in that it is only validated for certain classes of chemicals (i.e. acids, bases and certain derivatives).

In general the test cannot accurately be applied to chemicals or substances that are aqueous and have a pH within a range of 4.5 to 8.5. In practice, this means a compatibility test is needed prior to performing the main test.

During validation it was however estimated that about 85% of solutions in this pH range were likely non-corrosive in animal tests.[/collapse]

Validation study

[collapsed]In the 1990s, the Corrositex method was evaluated on a number of occasions by agencies in the US. They concluded that in specific testing circumstances, the method would be useful as a stand-alone assay for evaluating skin corrosion potential.

A number of other US agencies have subsequently accepted the method as a replacement for animal tests for skin corrosion potential.

Concurrently in Europe, the Corrositex method was also included in both prevalidation and validation studies along with a number of other in vitro methods for assessing skin corrosion.

Specifically, the method was included the ECVAM International Validation Study on In Vitro Tests for Skin Corrosivity (1996 - 1997).[/collapse]

Validation study outcomes

[collapsed]Validation studies carried out by EURL ECVAM on the Corrositex method demonstrated acceptable intra- and inter-laboratory reproducibility.[/collapse]

EURL ECVAM recommendations

[collapsed]On the basis of the outcomes of the validation studies, it was concluded that the test did not in fact meet all of the pre-defined criteria for acceptance of the method as a replacement for animal-based testing for the skin corrosion.

However, for certain classes of chemicals - organic bases and inorganic acids - the test appeared valid. On that basis the EURL ECVAM Scientific Advisory Committee (ESAC) endorsed a statement that the method was scientifically validated, but only for those acids, bases and derivatives that met the technical requirements of the assay.

Subsequent developments have included further regulatory approvals in the US and the adoption of an OECD test guideline (No 435) that is applicable to the Corrositex method.[/collapse]