FVR – Feline Viral Rhinotracheitis

Feline Viral Rhinotracheitis and URI Research(1), Trials, and USDA Regulations.

As a distributor, VetImmune® does not run clinical trials. Because veterinarians and customers often ask questions about Polyprenyl Immunostimulant™ trials, we are listing past, current, and planned Sass & Sass, Inc. clinical studies and trials that involve Polyprenyl Immunostimulant™ (PI, PPI).

Feline viral rhinotracheitis (FVR), a common and ubiquitous upper respiratory infection (URI), was the target of Sass & Sass, Inc. initial research and development. The disease is caused by FRV, which belongs to herpesviruses. The virus is easily transmitted between the cats in multi-cat environments, and the disease is ubiquitous.

Sass & Sass, Inc. Polyprenyl Immunostimulant™ Research and Development timeline & benchmarks (FRV.)


Ongoing preclinical research

Sass & Sass, Inc. starts preclinical research in vitro, toxicity studies and safety while developing a method for the manufacturing of Polyprenyl Immunostimulant™. In 2002, based on the presented data, USDA agrees to regulate the product. Molecular and biochemical research with Polyprenyl Immunostimulant™ is ongoing.

2006 - 2013

First clinical trials

Sass & Sass, Inc. conducted three clinical double-blinded, randomized, placebo-controlled clinical trials of the efficacy of Polyprenyl Immunostimulant™ (PI, PPI) in FVR in collaboration with, Dr. A.M. Legendre of the University of Tennessee-Knoxville (UTK), who was the Principal Investigator. The studies were performed by the team of UTK College of Veterinary Medicine (UTCVM) at the UTCVM Veterinary Research Facility (VRF) using specific pathogen-free cats(2).

2009 - 2010

Field Safety Study

Sass & Sass, Inc. carried out a field safety study in compliance with Title 9 CFR and approved by State Veterinarians of the 10 states where the study was conducted. This study was overseen by veterinarians working with the sample of 390 owned cats of any breed, sex, and age.


  • The results of the above studies were published in 2017 by A.M. Legendre, T. Kuritz, R.E. Heidel and V.M. Baylor in an open source peer reviewed article “Polyprenyl Immunostimulant in Feline Rhinotracheitis: Randomised Placebo-Controled Experimental and Field Safety Studies.

  • Based on the results of several USDA-compliant studies, Sass & Sass, Inc. successfully completed initial submission to the US Department of Agriculture (USDA). Following numerous rigorous reviews, the USDA granted the conditional license for Polyprenyl Immunostimulant™ after reviewing and accepting the data supporting the product safety and efficacy. Sass & Sass, Inc. subsequently performed, completed, and submitted to the USDA additional studies on the product potency.

As a result, Polyprenyl Immunostimulant™ becomes the first and only product used as a therapeutic for signs associated with feline rhinotracheitis (FVR), a disease caused by herpesvirus.

2009 - 2019

Continued research and trials on FVR and other PI (PPI) applications

Following USDA approval of Polyprenyl Immunstimulant™, Sass & Sass, Inc. continued research and trials on various applications and treatments in cats and other species:


  • In 2006-2009, Drs. Legendre and Bartges of UTK conducted and completed a preliminary pilot study on the survival times of cats with the dry (non-effusive) form of Feline Infectious Peritonitis (FIP) which was published in 2009.

  • In 2010-2011, Sass & Sass, Inc., in collaboration with Dr. Legendre of UTK, successfully conducted and completed a field study of the efficiency of Polyprenyl Immunostimulant in naturally occurring cases of non-effusive Feline Infectious Peritonitis (FIP). The results were published in 2017.

  • Since 2009, Sass & Sass, Inc. has been conducting case studies in cats with chronic rhinotracheitis treated with Polyprenyl Immunostimulant™. The manuscript has been submitted for publication.

  • In 2013, a small pilot study of the use of Polyprenyl Immunostimulant in the outbreak of canine distemper in ferrets was conducted at the Ferret Association of Connecticut.

  • In 2017, a clinical safety study of ocular topical application of Polyprenyl Immunostimulant™ by Dr. VanHorn Hendrix, UTK, established safety of the ocular topical formulation based on PI (PPI) and its results were presented at the meeting of the American College of Veterinary Ophthalmologists, October 2017, in Baltimore, MD.

  • Since 2018, Sass & Sass, Inc. has designed and is preparing to conduct a field efficacy study of Polyprenyl Immunostimulant™ in ocular herpetic disease, followng discussions with the USDA.

  • In 2019, Sass & Sass, Inc. conducted and completed a field study of upper respiratory infection (URI) in collaboration with the Planned Pethood facility in VA.

  • Currently, Sass & Sass, Inc. is planning pilot studies with its new candidate SS-07, its newest immunity modulator. SS07 was demonstrated to be safe in small studies with mice and cats.


(1) Results of research published in peer-reviewed journals cannot be used to substantiate health claims and do not substitute government regulated trials.

(2) Please note that under their ethics in clinical trials guidelines, Sass & Sass, Inc. believes that study animals should not be euthanized but should be provided a chance through adoption and be treated like any owned pet. Sass & Sass, Inc. does not purposely infect animals with fatal diseases and does not support any research that does.

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