Rose Bengal Sodium Shows Light-Independent Activity Against MRSA and Biofilms in New U.S. Patent, Expanding VisiRose's Ophthalmic Pipeline
Key Insights
Provectus and VisiRose (search) announced U.S. Patent No. 12,661,335 covering a topical rose bengal sodium eye drop formulation that kills resistant Gram-positive bacteria including MRSA (search) without requiring light activation.
The patent claims light-independent killing, biofilm eradication, and a defined tear-compatible formulation with a wide safety margin, enabling a self-administered eye drop for drug-resistant ocular infections.
The formulation addresses bacterial keratitis (search) caused by drug-resistant organisms, chronic blepharitis and conjunctivitis where biofilms limit antibiotic durability, and contact-lens-associated infections.
Provectus Biopharmaceuticals (search) and its ophthalmology subsidiary VisiRose (search) have been awarded U.S. Patent No. 12,661,335, titled "Halogenated Xanthene-Containing Topical Anti-Gram-Positive Bacterial Ophthalmic Composition and Method," the companies announced on June 30, 2026. The patent covers a topical eye drop formulation of pharmaceutical-grade rose bengal sodium (RBS) active pharmaceutical ingredient that kills resistant Gram-positive bacteria — including methicillin-resistant Staphylococcus aureus (MRSA (search)) and vancomycin-resistant Enterococcus (search) — and eradicates biofilms without requiring a light-activation step.
The newly issued patent, which stems from U.S. Application No. 18/089,134 filed December 27, 2022 and claims priority to a provisional application filed December 28, 2021, has the University of Tennessee Research Foundation as a co-assignee. VisiRose (search) will hold an exclusive license to develop and commercialize ophthalmic applications under its field license from Provectus.
Light-Independent Mechanism Opens Door to Self-Administered Therapy
The key differentiator of the patented formulation is its ability to exert antibacterial activity "in the substantial absence of activating light," according to the patent claims. This stands in contrast to VisiRose (search)'s investigational Rose Bengal Photodynamic Antimicrobial Therapy (RB-PDAT), which combines RBS with a green light medical device to treat infectious keratitis. A light-independent formulation can be prescribed, dispensed, and self-administered as a standard eye drop — the same use pattern as existing prescription antibiotic drops such as chloramphenicol or fluoroquinolones — but is aimed at resistant-organism infections those drugs increasingly cannot clear.
Ed Pershing, Chairman of VisiRose (search)'s Board of Directors and Chairman and CEO of Provectus, stated: "This patent gives us composition and method protection for a finding that matters deeply: rose bengal sodium can kill resistant Gram-positive bacteria, including MRSA (search), and eradicate their biofilms without a light-activation step. It's intellectual property that further strengthens the case for our proprietary rose bengal sodium as a platform molecule."
Patent Scope: Formulation, Spectrum, and Safety
The patent claims define a specific formulation with a concentration range of approximately 0.2 to 50 μg/mL and a pH of 6.5 to 7.6, matching normal human tear pH, along with specified viscosity and osmolality — parameters aimed at ocular tolerability and FDA formulation review. The claimed effective concentrations span methicillin- and vancomycin-resistant S. aureus as well as drug-resistant E. faecalis and E. faecium, organisms where first-line antibiotics are failing.
Critically, the patent covers biofilm eradication in both light and dark conditions. Chronic, recurrent ocular infections are often biofilm-driven and tolerant to standard antibiotics, including linezolid. In preclinical testing, the cytotoxicity threshold in mammalian cells sat well above the concentrations needed to kill resistant bacteria, providing a safety margin that supports repeat dosing.
Clinical and Market Implications
The light-independent formulation directly addresses several unmet needs in ocular infectious disease. Bacterial keratitis (search) caused by drug-resistant Gram-positive organisms remains a leading cause of preventable corneal blindness and is a recurring diagnosis in contact lens wearers. The formulation also targets chronic and recurrent blepharitis and conjunctivitis, where biofilm tolerance limits the durability of standard antibiotic regimens. For contact-lens-associated infections, a take-home, light-free drop represents a meaningfully different treatment experience compared to photodynamic therapy requiring a clinical visit.
RBS serves as the proprietary synthetic small molecule and API underlying Provectus's clinical-stage oncology and dermatology programs as well as VisiRose (search)'s clinical-stage ophthalmology program. The patent award extends the platform's ophthalmology intellectual property footprint.
The safety and efficacy of the agents and uses under investigation have not been established, and there is no guarantee that the agents will receive health authority approval or become commercially available in any country for the uses being investigated.