Rose bengal sodium patent targets drug-resistant keratitis

Patent covers resistant bacteria

According to a new announcement, Provectus Biopharmaceuticals, Inc. and its ophthalmology subsidiary VisiRose, Inc. secured US Patent No. 12,661,335 for a light-independent antibacterial eye drop formulation of rose bengal sodium (RBS).¹ The patent covers a topical treatment for Gram-positive bacterial keratitis, including drug-resistant strains such as methicillin-resistant Staphylococcus aureus (MRSA) and vancomycin-resistant Enterococcus.¹ VisiRose holds an exclusive ophthalmic license to develop and commercialize the claimed applications.¹

The finding gives optometrists a new pathway toward prescribing a self-administered drop against resistant organisms, rather than relying on a device-based photodynamic procedure.¹ Standard antibiotic drops increasingly fail against resistant Gram-positive bacteria, leaving few options ODs can prescribe directly for recurrent anterior segment infections in contact lens wearers and other patients.¹

Patent No. 12,661,335, titled "Halogenated Xanthene-Containing Topical Anti-Gram-Positive Bacterial Ophthalmic Composition and Method," claims antibacterial activity in the substantial absence of activating light.¹ Claimed effective concentrations span methicillin- and vancomycin-resistant S. aureus along with drug-resistant Enterococcus faecalis and Enterococcus faecium, organisms where first-line antibiotics are failing.¹ The composition also eradicates biofilms in both light and dark conditions, addressing chronic, recurrent infections tolerant to standard antibiotics, including linezolid.¹

Formulation claims fix concentration at approximately 0.2 to 50 mcg per mL and pH between 6.5 and 7.6, matching normal human tear pH, along with defined viscosity and osmolality specifications aimed at ocular tolerability.¹ In preclinical testing, the cytotoxicity threshold in mammalian cells sat well above the concentrations needed to kill resistant bacteria, a margin a topical product would need to support repeat dosing.¹

Patent and pipeline context

The University of Tennessee Research Foundation is a co-assignee on the patent, which issued from an application filed December 27, 2022, claiming priority to a provisional filed December 28, 2021.¹ RBS is the synthetic small molecule underlying Provectus's oncology and dermatology programs and VisiRose's ophthalmology program, and the new patent extends the platform's ophthalmic intellectual property footprint.¹

A light-independent formulation is structurally closer to a standard eye drop than the light-activated photodynamic therapy VisiRose has previously pursued for infectious keratitis, and could in principle be prescribed and self-administered the way chloramphenicol or fluoroquinolone drops are today.¹ Independent coverage of the announcement confirmed the patent number and claim scope, adding context on the broader RBS-based pipeline spanning oncology, dermatology, and ophthalmology.² Researchers from Bascom Palmer Eye Institute presented preclinical data on MRSA biofilm inhibition using rose bengal photodynamic antimicrobial therapy at the 2026 Association for Research in Vision and Ophthalmology meeting, work that underlies the resistant-organism claims in the new patent.³

Ed Pershing, chairman of the VisiRose board and chairman and chief executive officer of Provectus, said the patent offers composition and method protection for rose bengal sodium's demonstrated ability to kill resistant Gram-positive bacteria, including MRSA, and eradicate biofilms without a light-activation step.¹

References:

1. Provectus Biopharmaceuticals and VisiRose announce U.S. patent award for light-independent antibacterial eye drop targeting drug-resistant ocular infections. Provectus Biopharmaceuticals, Inc. Press release. June 30, 2026. Accessed July 10, 2026. https://www.biospace.com/press-releases/provectus-biopharmaceuticals-and-visirose-announce-u-s-patent-award-for-light-independent-antibacterial-eye-drop-targeting-drug-resistant-ocular-infections

2. Provectus (PVCT) secures patent for innovative eye drop treatment. GuruFocus. July 2026.

3. Bascom Palmer Eye Institute presents four posters on rose bengal photodynamic antimicrobial therapy at ARVO 2026. Provectus Biopharmaceuticals, Inc. Press release. May 4, 2026. Accessed July 10, 2026. https://www.provectusbio.com/news/press-releases/bascom_palmer_eye_institute_presents_four_posters_on_rose_bengal_photodynamic_antimicrobial_therapy_at_arvo_2026/