MICHAEL E. HERBIG
Co-founder and CEO, RaDes GmbH, Hamburg, Germany

Abstract

It is widely accepted that excipients play a crucial role in efficacy, safety and quality of medicinal products. For topical drug delivery, there are particular aspects to consider. Excipients are responsible for the perception of the product by the patient and directly impact on well-being and adherence to the therapy. They can have a direct impact on the efficacy, e.g. through moisturizing or antimicrobial effects. Indirectly, they can influence efficacy through chemical penetration enhancement. More than 500 excipients are approved for topical drug delivery by the FDA. Many of them are complex and show substantial variability in potentially critical material attributes, which may affect the quality of the resulting drug product. Therefore, appropriate characterization is essential for the development of robust products.

PARTICULAR ASPECTS OF EXCIPIENTS FOR TOPICAL DRUG FORMULATIONS
Across dosage forms and routes of administration, it is now generally accepted that excipients cannot be regarded simply as inert or inactive ingredients. A detailed knowledge about these materials is essential for efficient and successful drug product development (1). Excipients are substances other than the API (active pharmaceutical ingredient) that are intentionally included in a drug delivery system. Excipients are similarly strictly regulated as APIs. They can only be used if appropriately evaluated for safety and released according to the requirements of GMP. Some of their general functions in medicinal products include supporting formulatability and processability, contributing to or improving stability of the API, ensuring bioavailability, and supporting compliance by patient friendly dosage forms.

For topical drug formulations, several particular aspects can be identified. The perception of the vehicle created from the selected excipients is especially important. Much more than for example a tablet, topical vehicles are sensorially perceptible and may directly ...