Abstract
The efficacy of topical drug delivery via eye drops is often achieved at the expense of tolerability, and consequently, efforts are being made to design strategies that minimize the adverse effects associated with the passage of active pharmaceutical ingredients (APIs) across the ocular surface. Many of these approaches are too complex, costly and challenging to implement on an industrial scale, yet there is increasing evidence that hylan A, a very high molecular weight hyaluronic acid (≥3.0 MDa), may be a promising vehicle for topical drug delivery of ocular therapies. In this review, we explore how the mucoadhesive and viscoelastic properties of eye drop formulations based on hylan A help extend the residence time of APIs at the ocular surface, while maintaining patient comfort. Moreover, we examine how hylan A facilitates the dissolution and stabilization of APIs, as well as their transport across the ocular epithelial barrier, without the need to use toxic penetration enhancers, thereby preserving ocular surface health. Finally, we present evidence indicating that the intrinsic biological properties of hylan A, including its anti-inflammatory effects, help mitigate side effects commonly associated with certain APIs. To illustrate these advantages, we examine the pioneering use of a hylan A-based aqueous eye drop formulation as a vehicle to deliver latanoprost, a prostaglandin analogue widely used in the treatment of glaucoma. This case study demonstrates the potential of hylan A-based eye drops to offer safer and more effective topical drug delivery, especially for long-term ocular therapies where tolerability and biocompatibility are critical.