Field Trial of Polyprenyl Immunostimulant in Cats with Noneffusive Feline Infectious Peritonitis

April 10, 2017
Laurie Anne Walden, DVM, ELS

Dr. Walden received her doctorate in veterinary medicine from North Carolina State University. She is a practicing veterinarian and a certified editor in the life sciences (ELS). She owns Walden Medical Writing, LLC, and writes and edits materials for healthcare professionals and the general public.

Polyprenyl immunostimulant may improve survival time and quality of life in cats with noneffusive feline infectious peritonitis.

Polyprenyl immunostimulant (PI) may improve survival time and quality of life in cats with noneffusive feline infectious peritonitis (FIP), say the authors of a report recently published in Frontiers in Veterinary Science.1 A controlled study is needed to verify the findings, they write.

PI is a veterinary biological product with a US Department of Agriculture conditional license for symptomatic treatment of feline rhinotracheitis virus infection. Previous studies by the research group, led by Alfred Legendre, DVM, MS, DACVIM (University of Tennessee College of Veterinary Medicine), indicated that the product might benefit cats with the dry form of FIP. PI boosts cell-mediated immunity and could theoretically be used to treat diseases in which cellular immunity is suppressed, like FIP.

The treatment is controversial, however. The University of California Davis School of Veterinary Medicine lists PI as “not recommended” for cats with FIP, citing a lack of substantial evidence for its efficacy. “Based on the results that have been presented to date, the [Center for Companion Animal Health] cannot recommend PI as a means to treat or even prolong life in cats with any form of FIP,” reads a statement on the school’s website.2

The field study included 60 cats diagnosed with noneffusive FIP. Cats included were from the United States and Canada and had clinical signs and diagnostic test results (complete blood count, blood chemistry profile, feline coronavirus antibody titers, and, in some cases, histology) consistent with a diagnosis of FIP. Cats were excluded if they died before receiving the first dose of PI, treatment was discontinued after 1 or 2 doses, they had effusive FIP, or they did not return for follow-up examinations.

Participating cats received 3 mg/kg of PI by mouth 3 times a week and were evaluated by their veterinarians periodically (the investigators recommended monthly follow-up examinations). Cats could receive other treatments during the course of the study, but the researchers recommended not using corticosteroids because of their immunosuppressive effect. To avoid withholding potentially beneficial treatment from cats with a serious disease, the investigators did not include a control group.

Of the 60 cats that received PI, 8 survived longer than 200 days and 4 survived longer than 300 days. The survival times in these cats were longer than have been reported previously for cats with noneffusive FIP, say the authors. Cats receiving corticosteroids concurrently with PI had a significantly shorter median survival time (21.5 days) than cats not receiving corticosteroids (73.5 days).

The investigators gathered quality of life information from communication with veterinarians and cat owners and from notes entered in the cats’ medical records. These reports all indicated that the cats’ quality of life had improved, they write. In general, say the authors, cats receiving PI returned to mostly normal activities (with occasional exceptions) until they underwent a rapid decline that resulted in death or euthanasia.

“Our results suggest that PI benefits cats clinically diagnosed with dry FIP by increasing survival times and improving quality of life but a controlled study will be needed to verify the benefit of PI in the treatment of FIP,” conclude the investigators. They add that PI is not a cure but might allow some cats to maintain noneffusive FIP as a chronic condition.

Dr. Laurie Anne Walden received her doctorate in veterinary medicine from North Carolina State University. After an internship in small animal medicine and surgery at Auburn University, she returned to North Carolina, where she has been in small animal primary care practice for over 20 years. Dr. Walden is also a board-certified editor in the life sciences and owner of Walden Medical Writing, LLC. She works as a full-time freelance medical writer and editor and continues to see patients a few days each month.


  • Legendre AM, Kuritz T, Galyon G, Baylor VM, Heidel RE. Polyprenyl immunostimulant treatment of cats with presumptive non-effusive feline infectious peritonitis in a field study. Front Vet Sci. 2017;4:7.
  • FIP and polyprenyl immunostimulant (PI). UC Davis Veterinary Medicine website. Accessed April 6, 2017.