Astaxanthin Delivery Across Administration Routes: Recent Advances to Improve Stability and Bioavailability

Astaxanthin (ASX) is a xanthophyll carotenoid widely studied for its beneficial properties in humans, mainly related to its local or systemic antioxidant, cytoprotective and immunomodulatory effects. Particularly, ASX can donate electrons to neutralize reactive oxygen species (ROS), thereby mitigating oxidative stress, a key factor in the onset of several chronic and degenerative diseases. Thanks to these valuable properties, ASX has attracted considerable interest in the pharmaceutical, nutraceutical and cosmetic sectors. Despite its promising biological potential, the application of ASX is limited by several physicochemical factors. It is a highly lipophilic molecule, unstable when exposed to light, heat and oxygen, which leads to rapid degradation, and is characterized by low bioavailability. To overcome these limitations, various formulation strategies have been developed, particularly encapsulation-based approaches aimed at improving stability, solubility and therapeutic applications. This review provides an overview of the conventional and innovative dosage forms of ASX developed to enhance bioavailability and preserve the chemical and biological properties of this powerful antioxidant, by focusing on the different administration routes. Special attention is given to the advantages and limitations of the different formulation strategies and their implications for human health according to the different administration routes. Although oral administration remains the most explored route, further studies are needed to develop formulations suitable for alternative routes of administration.