Why sustained release is the defining challenge in wet AMD treatment
Neovascular (wet) age-related macular degeneration is driven by pathological growth of blood vessels beneath the retina — a process mediated by vascular endothelial growth factor (VEGF) and its downstream tyrosine kinase signalling cascades. Current standard-of-care anti-VEGF biologics require intravitreal injections every four to twelve weeks, imposing a significant treatment burden on patients and healthcare systems. The central question confronting drug developers, as evidenced by a dense cluster of patent filings from 2021 to 2024, is not whether to pursue sustained release — but which delivery architecture will win.
The axitinib intravitreal implant approach targets this problem at the molecular level. Axitinib is a potent, selective inhibitor of VEGF receptors 1, 2, and 3, as well as PDGF receptors — a multi-target profile that has attracted sustained patent investment from Ocular Therapeutix and, increasingly, from a global cohort of competitors. According to WHO, age-related macular degeneration is a leading cause of vision loss in people over 50, making the commercial stakes for a truly long-acting treatment exceptionally high.
Axitinib-containing sustained release ocular implants are designed to treat neovascular age-related macular degeneration (wet AMD) and other ocular conditions by delivering the VEGF receptor tyrosine kinase inhibitor axitinib directly into the vitreous over an extended period, reducing the need for repeated intravitreal injections.
The polymer science underpinning these implants is also a source of competitive differentiation. Poly(lactic-co-glycolic acid) — PLGA — has emerged as the dominant matrix material, described in filings from Ocular Therapeutix, Shanghai Ruyuan Pharmaceutical Technology, and the University of Colorado, among others. PLGA degrades hydrolytically in the body, releasing encapsulated drug as the polymer erodes — a mechanism that aligns naturally with a bioerodible depot strategy. Research published by Nature and peer-reviewed ophthalmic journals has documented PLGA’s biocompatibility profile in ocular tissues, supporting its use as a preferred excipient in this indication.
Ocular Therapeutix’s axitinib implant patent position: scope and structure
Ocular Therapeutix, Inc. is the single most prolific assignee in the axitinib intravitreal implant space, with a filing series that spans US, WO, and EP jurisdictions and covers both the composition and methods of use for axitinib-containing sustained release ocular implants. The earliest filings in this cluster date to 2021, with the PCT application WO2021178473A1 published in September 2021 and the US national phase US20210236384A1 published in August 2021. The company has since obtained at least two granted US patents — US11382909B2 (granted July 2022) and US12016871B2 (granted June 2024) — with additional continuation applications published as recently as October 2024 (US20240325284A1).
OTX-TKI is the investigational name used for Ocular Therapeutix’s axitinib intravitreal implant programme. The implants described in the company’s patents comprise axitinib and a poly(lactic-co-glycolic acid) (PLGA) polymer matrix, are solid and rod-shaped in some embodiments, and are configured for intravitreal administration via a 25-gauge or smaller needle — enabling in-office delivery without surgical implantation.
The claims architecture across the Ocular Therapeutix filings is broad. The composition claims cover axitinib-containing sustained release drug delivery ocular implants as a class, while method claims cover treating age-related macular degeneration and other ocular conditions using those implants. A notable 2023 filing (US20230390183A1) explicitly describes injectable microparticle formulations comprising axitinib and PLGA alongside solid rod-shaped implant embodiments — suggesting the company is protecting both a depot-injection format and a larger implant format within the same patent family.
The European Patent Office filing EP4117635A1, published January 2023, extends the Ocular Therapeutix footprint into European markets — a critical jurisdiction given the prevalence of wet AMD in ageing European populations. The EP application covers the same core axitinib-containing sustained release implant technology, indicating a deliberate multi-jurisdictional prosecution strategy consistent with commercial intent to seek approval in both the US and EU. According to EPO filing data, the ophthalmic drug delivery sector has seen sustained growth in PCT and EP-phase filings, reflecting the commercial value of European market exclusivity in chronic ocular disease.
Ocular Therapeutix, Inc. has obtained at least two granted US patents for axitinib-containing sustained release ocular implants: US11382909B2 (granted July 2022) and US12016871B2 (granted June 2024), with continuation applications published as recently as October 2024 (US20240325284A1).
Bioerodible depot vs. port delivery: two competing architectures
The sustained-release ocular implant field has coalesced around two fundamentally different engineering philosophies, each with distinct IP, clinical, and commercial implications. Understanding how they differ is essential for assessing the competitive dynamics that Ocular Therapeutix’s axitinib implant programme must navigate.
The bioerodible depot approach
A bioerodible depot is an implant that degrades within the eye over time, releasing drug as the polymer matrix erodes — and then disappearing entirely, requiring no surgical removal. The PLGA-based axitinib implants described in Ocular Therapeutix’s filings exemplify this approach. Patent US20230390183A1 describes both solid rod-shaped implants and injectable microparticle formulations comprising axitinib and PLGA, configured for intravitreal administration via a 25-gauge or smaller needle. The 25G delivery format is clinically significant: it means the implant can be placed during a standard in-office intravitreal injection procedure, without the surgical intervention required for a port delivery system.
“Some axitinib intravitreal implants are configured for intravitreal placement via a 25-gauge or smaller needle — enabling in-office delivery without surgical implantation.”
Chinese assignee Shanghai Ruyuan Pharmaceutical Technology (CN116440073A, published July 2023) describes a solid rod-type axitinib/PLGA implant where the weight ratio of axitinib to PLGA ranges from 1:0.1 to 1:9, with a preferred range of 1:1 to 1:3. The implant can be injected intravitreally with a 25-27G needle and sustains in vitro release for 1 to 12 months, with in vivo release of more than 3 months and preferably more than 6 months. Chengdu Kanghong Pharmaceutical (CN115569093A) takes a different excipient approach, specifying axitinib content of 50–99% by weight (preferably 70–99%) with particle sizes of 1–100 μm, using excipients including PLGA, PLA, PEG, and polycaprolactone.
The non-erodible and refillable port delivery approach
The port delivery system represents the alternative architecture: a surgically implanted, non-erodible reservoir that can be refilled with drug during an in-office procedure. EyePoint Pharmaceuticals (US20210338581A1, US20210007990A1) describes intravitreal TKI implants configured to release drug for at least 12 months following administration, using water-insoluble polymer compositions suitable for both non-erodible and bioerodible sustained release formulations. Celanese Eva Performance Polymers (US20230129018A1) describes an ocular drug delivery implant with a drug core in a polymeric matrix — using EVA (ethylene-vinyl acetate) as the polymer — configured to provide controlled release for at least 6 months, at least 12 months, or at least 24 months.
EyePoint Pharmaceuticals claims at least 12 months of TKI release from intravitreal implants. Celanese Eva Performance Polymers claims up to 24 months. Shanghai Ruyuan’s PLGA rod targets more than 6 months in vivo. These duration claims are central to the competitive differentiation between programmes and will likely be a focus of both patent prosecution and clinical trial design.
Allergan, Inc. (now part of AbbVie) has also entered the bioerodible implant space with a distinct technical approach: two filings (US20230048501A1 and US20230165854A1) describe intravitreal implants comprising large crystals of a TKI — specifically axitinib or pazopanib — embedded in a bioerodible polymer matrix. The large-crystal formulation strategy is designed to slow drug dissolution and extend release duration, representing a crystalline-drug variant on the PLGA depot theme. This approach is protected by separate claims that do not overlap directly with the Ocular Therapeutix microparticle or rod-shaped implant claims, illustrating how multiple assignees can pursue differentiated IP positions within the same therapeutic space.
Explore the full axitinib intravitreal implant patent landscape in PatSnap Eureka — including claim maps, assignee timelines, and freedom-to-operate signals.
Analyse Patents with PatSnap Eureka →The competitive TKI intravitreal implant landscape: who else is filing
Beyond Ocular Therapeutix, at least seven other assignees have filed patents for TKI-based intravitreal implants — several of which explicitly name axitinib as a preferred compound. The landscape spans US, WO, EP, and CN jurisdictions, with Chinese assignees representing a notable and growing presence.
Kodiak Sciences (US20230158185A1, published May 2023) describes a bioerodible sustained-release drug delivery system for delivering a TKI to the vitreous and/or retina, targeting ocular conditions including AMD and diabetic retinopathy. The University of Colorado (US20240197662A1, published June 2024) takes a photocrosslinkable polymer approach, describing a composition comprising a poly(ethylene glycol) diacrylate (PEGDA) polymer matrix and PLGA-based nanoparticles encapsulating axitinib — a nanoparticle-in-hydrogel architecture that differs structurally from the rod-type or microparticle approaches used by commercial assignees.
At least eight distinct assignees — including Ocular Therapeutix, EyePoint Pharmaceuticals, Allergan, Kodiak Sciences, Celanese Eva Performance Polymers, Chengdu Kanghong Pharmaceutical, Shanghai Ruyuan Pharmaceutical Technology, and the University of Colorado — have filed patents for axitinib-containing or TKI-based intravitreal implants for wet AMD across US, WO, EP, and CN jurisdictions.
The presence of Allergan (now AbbVie) in this space is strategically significant. Allergan’s large-crystal TKI implant filings (US20230048501A1, US20230165854A1) name both axitinib and pazopanib as preferred compounds, and the bioerodible polymer matrix approach overlaps technically — though not in claim scope — with the Ocular Therapeutix PLGA depot strategy. AbbVie’s resources and ophthalmology commercial infrastructure mean that any Allergan-derived programme reaching clinical proof-of-concept would represent a formidable competitive threat to Ocular Therapeutix’s first-mover position.
Map claim overlaps and freedom-to-operate risks across the TKI intravitreal implant space with PatSnap Eureka’s AI-powered patent analysis.
Explore Full Patent Data in PatSnap Eureka →IP implications for drug developers and retinal therapeutics investors
The axitinib intravitreal implant patent landscape carries several strategic implications for IP professionals, R&D leaders, and investors tracking the wet AMD pipeline. The density of Ocular Therapeutix’s filing programme — spanning composition, method of use, and manufacturing claims across US, WO, and EP — creates a substantial barrier to direct entry for competitors seeking to commercialise an axitinib/PLGA depot in the same format. However, the existence of differentiated technical approaches (large-crystal formulations from Allergan, nanoparticle-in-hydrogel from University of Colorado, EVA-based non-erodible implants from Celanese) demonstrates that the space is not monolithic and that workaround strategies exist.
For patent attorneys conducting freedom-to-operate analyses, the key distinctions to map include: (1) the physical form of the implant (rod-shaped solid vs. microparticle vs. large-crystal vs. nanoparticle-in-hydrogel); (2) the polymer matrix composition (PLGA vs. EVA vs. PEGDA vs. polycaprolactone); (3) the delivery gauge and mechanism (25G injectable vs. surgical implantation); and (4) the claimed release duration (months vs. years). Each of these axes represents a potential claim differentiation point that could support a non-infringing product design or a validity challenge to a competitor’s granted claims. The USPTO‘s examination of continuation applications in this family will be closely watched, given the breadth of the parent claims in US11382909B2 and US12016871B2.
Axitinib intravitreal implant patents from Ocular Therapeutix include both solid rod-shaped implant embodiments and injectable microparticle formulations comprising axitinib and PLGA, with some claims covering intravitreal placement via a 25-gauge or smaller needle — a clinically significant feature that enables in-office delivery without surgical implantation.
For investors, the continuation filing activity through 2024 (US20240325284A1, US20240108583A1) signals that Ocular Therapeutix is actively prosecuting claims that may extend the effective patent life of the programme well beyond the priority dates of the 2021 PCT filings. Continuation practice at the PatSnap IP intelligence platform level allows assignees to introduce new claims that track the evolving claim scope of competitors — a dynamic that will be critical to monitor as the competitive landscape matures. The WIPO PCT system provides a 30-month window for national phase entry, meaning that WO2021178473A1’s 2021 filing date anchors priority for jurisdictions that may not yet have published national phase applications.
The Chinese patent filings from Chengdu Kanghong and Shanghai Ruyuan are also noteworthy from a market access perspective. China represents one of the largest and fastest-growing markets for ophthalmic therapeutics, and domestic Chinese assignees filing axitinib intravitreal implant patents suggest that local regulatory and commercial strategies are being developed in parallel with Western programmes. The axitinib content specifications in CN115569093A (50–99% by weight, preferably 70–99%) differ from the PLGA-matrix-dominant approaches of Western assignees, potentially reflecting both formulation preferences and strategic claim differentiation relative to the Ocular Therapeutix portfolio.