The OECD 402 Acute Dermal Toxicity test is used to assess the potential short-term hazards of a chemical substance when exposed through the skin (dermal exposure), in order to support classification and labeling. The study design follows the current OECD Test Guideline 402 entitled “Acute Dermal Toxicity: Fixed Dose Procedure” and is typically performed on rats and in accordance with Good Laboratory Practice regulations.  This test is part of the Acute Toxicity Six-Pack tests.

How the OECD 402 Acute Dermal Toxicity Test is Performed

Within the guidance, two main types of tests are outlined for assessing acute dermal toxicity: limit tests and full tests.

The limit test aims to quickly determine if the test article has very low acute dermal toxicity without conducting a full dose-response study. It involves using a single dose level and a small number of animals per group. If no signs of toxicity or mortality are observed, the substance is deemed to have low toxicity, meaning that you would not need to subsequently perform a full test. However, if toxicity is observed, a full test becomes necessary to generate data suitable for regulatory use.

The full test provides a comprehensive assessment of acute dermal toxicity by establishing a dose-response relationship. Multiple dose levels are used, and a larger number of animals are typically employed to ensure statistical validity. The animals are observed over a specified period to monitor signs of toxicity, mortality, and calculate the LD50 value. This approach generates detailed toxicity data that is valuable for risk assessment and regulatory submissions.

To run OECD 402, the test article is applied over a shaved area of skin which is approximately 10 per cent of the total body surface area and held in contact with the skin for a 24 hour period. Animals are observed daily for at least 14 days and the weights of the animals are determined at least weekly. All animals are subjected to a gross necropsy at the end of the study.

How to Choose between the Limit Test and the Full Test

Both limit tests and full tests are considered valid approaches in the OECD 402 guidance. The choice between them depends on factors such as the available data, regulatory requirements, and the nature of the test substance. Limit tests are faster and less resource-intensive, making them suitable for screening out substances with very low toxicity. In contrast, full tests offer a more in-depth analysis and are required when detailed toxicity data is needed or when a substance shows signs of toxicity in the limit test.

Typically 10 grams of test article are required. This test is performed in compliance with Good Laboratory Practice Regulations.