“How Irritating!” A new paradigm for irritation testing

Author: James Morrison

In January 2021, a new biocompatibility standard was published: ISO 10993-23 Biological evaluation of medical devices – Tests for irritation. This has been long-anticipated and is a very welcome event.

Prior to publication, irritation was evaluated according to ISO 10993-10 Biological evaluation of medical devices – Tests for irritation and skin sensitization. An immanent revision of Part 10 will include only tests for skin sensitization.

Part 23 sees the introduction of an in vitro irritation model, validated for medical devices, the Reconstituted Human Epithelium (RhE) test. This test effectively replaces the commonly used, in vivo: Animal irritation (Draize) test and Animal intracutaneous (intradermal) reactivity test. This is an excellent development, particularly in terms of animal welfare. It will greatly reduce the use of animals used in irritation testing.

The RhE test is not universally useful. There are still particular situations that require in vivo tests, for example, contact with specific areas (mucosal membrane) or devices not suitable for extraction. However, it is important to note that Part 23 requires: “the in vitro irritation test shall be performed before animal testing or human patch test is considered.” Where the RhE test is appropriate, it must be used first to evaluate irritation. In vivo test methods are only appropriate (permissible) in Part 23 if the RhE test is not able to establish the irritation outcome.

Clearly, the industry is anxiously waiting for US FDA to recognise ISO 10993-23:2021, and to understand the extent of that recognition. As a major regulatory consumer of irritation test results, FDA recognition will largely determine the reduction in animal testing.

Manufacturers would be well advised to discuss the new test method with their biocompatibility testing suppliers. (As well as studying Part 23!) Particularly: understanding, interpreting and evaluating the test results are new skills to be developed, and ultimately applied.