White paper: Understanding, informing and defining the regulatory science of microneedle-based dosage forms that are applied to the skin.

The COVID-19 pandemic has accelerated pre-clinical and clinical development of microneedle-based drug delivery technology. However the regulatory science of this emerging dosage form is immature and explicit regulatory guidance is limited. A group of international stakeholders has formed to identify and address key issues for the regulatory science of future products that combine a microneedle device and active pharmaceutical ingredient (in solid or semi-solid state) in a single entity that is designed for application to the skin. Guided by the principles of Quality by Design (QbD) and informed by consultation with wider stakeholders, this 'White Paper' describes fundamental elements of the work in an effort to harmonise understanding, stimulate discussion and guide innovation. The paper discusses classification of the dosage form (combination/medicinal product), the regulatory nomenclature that is likely to be adopted and the technical vocabulary that best describes its form and function. More than twenty potential critical quality attributes (CQAs) are identified for the dosage form, and a prioritisation exercise identifies those CQAs that are most pertinent to the dosage form and that will likely require bespoke test methods (delivered dose, puncture performance) or major adaptions to established compendial test methods (dissolution). Hopefully the work will provide a platform for the development of dosage form specific guidance (from regulatory authorities and/or international pharmacopoeias), that expedites clinical translation of safe and effective microneedle-based products.