Diagnostic gap due to missing patch test allergens—status quo and possible scenarios for mitigation

Summary According to European Directive 2001/83/EC, test and therapeutic allergens are medicinal products in all Member States of the European Union. This applies equally to prick test and to patch test (PT) allergens (haptens). All test allergens commercially marketed in Germany are finished medicinal products requiring marketing authorization (MA). Currently, 211 PT substances are authorized in Germany, and an additional 59 are in an ongoing MA process and are marketable under a transitional provision until a decision on MA is made. The regulatory guidance (CMDh/399/2019) of the Co-ordination Group for Mutual Recognition and Decentralized Procedures—Human (CMDh), published in July 2020, specifies the regulatory requirements for different allergen products. Due to differences in origin and exposure, use, mode of action, and safety risks, the guideline clearly differentiates between products with active ingredients of biological origin (allergen extracts from natural source materials) and products with active ingredients of non-biological origin (hapten-based PT substances). Currently, guideline-compliant patch testing is hampered by the lack of numerous commercial PT allergens from the standard and special test series. Background and possible scenarios for mitigation are presented here.