October 27, 2025 – A cream originally developed for human cold sores may soon become a game-changer for cats battling eye infections, according to researchers at the Hebrew University of Jerusalem (HU). 

Feline herpesvirus type 1 (FHV-1) is one of the most common causes of eye disease in cats, often leading to chronic infections, discomfort, and vision problems. Standard antiviral treatments, such as oral famciclovir, can be difficult for owners to administer and have limited absorption in cats. 

According to the study published in Veterinary Science—led by Dr. Oren Pe’er, together with Dr. Lionel Sebbag and Prof. Ron Ofri from the Ophthalmology Department at HU’s Koret School of Veterinary Medicine and in collaboration with Prof. Sara Thomasy and her team at the School of Veterinary Medicine at the University of California, Davis—found that a 1% penciclovir cream commonly used in human dermatology (Fenlips®) is safe, well-tolerated, and effective when used to treat eye infections caused by feline herpesvirus type 1 (FHV-1). 

“Our findings suggest that a simple over-the-counter cream could offer an easier, effective option for cat owners struggling to manage recurrent eye infections,” said Dr. Pe’er. “This means twice-daily application could be enough to keep the virus in check, which is a major step toward improving both animal welfare and treatment compliance.” 

In the retrospective survey, most cat owners reported excellent tolerance and visible improvement when using Fenlips®, with 85% noting no side effects and 80% rating the treatment as effective or highly effective. To confirm safety and effectiveness, the researchers conducted additional studies in healthy cats over a month-long period. No adverse reactions were observed, and tear tests showed that penciclovir levels stayed above the concentration needed to inhibit the herpesvirus for over eight hours after application. 

The researchers emphasize that while the results are encouraging, further studies in larger patient populations are needed before the treatment can be formally approved for ophthalmic use in cats. 

The research paper titled “Ocular tolerance and tear film pharmacokinetics of 1 % penciclovir cream in cats” is now available in Veterinary Science and can be accessed here.

Researchers:

Oren Pe’er¹, Sara M. Thomasy², Eliana. Feuer¹, Heather .K. Knych³, Ron Ofri¹, Lionel Sebbag¹

Institutions:

1. Koret School of Veterinary Medicine, The Hebrew University of Jerusalem
2. Department of Surgical and Radiological Sciences, School of Veterinary Medicine, University of California-Davis
3. Department of Molecular Biosciences, School of Veterinary Medicine, University of California-Davis