FIP and Polyprenyl Immunostimulant (PI)

Original article: FIP and Polyprenyl immunostimulant (PI) published on the UC Davis website.

Based on the results presented so far, CCAH cannot recommend PI as a means of prolonging the life of cats in any form of FIP.

Polyprenyl Immunostimulant

Polyprenyl immunostimulant (PI) is classified as a biopharmaceutical by the USDA and is manufactured by Sass and Sass in Tennessee. PI received a conditional license from the USDA as a therapeutic to treat the "symptoms" of feline herpesvirus infection. According to the Sass and Sass websites, they are conducting research into its use in the treatment of FIP and other pet diseases. Although not approved by the USDA for the treatment of FIP, it is currently commonly used to prolong the lives of cats with milder forms of FIP. It has not shown any benefit in the treatment or prolongation of the life of cats with wet FIP or cats with signs of serious illness at the beginning of treatment. Although, according to the web and according to some individuals, it provides an opportunity to prolong the life of cats with FIP, especially milder dry forms, it is important to examine what is known about the effectiveness of PI when used for this purpose. For a cat of average size and with a standard dosage, PI can cost more than $ 400 a month, and these costs can add to the associated veterinary expenses.

The first report on the use of PIs for the treatment of FIP was an article Effect of Polyprenyl Immunostimulant on the survival times of three cats with the dry form of feline infectious peritonitispublished by Dr. Al Legendre and colleagues in 2009. This study included three cats with dry FIP treated with polyprenyl immunostimulant. Two of the three cats were still on treatment and alive and well 2 years after diagnosis. The third cat survived 14 months, but was treated for only 4.5 months. However, it is important to know that these three cats suffered from a disease limited to the intestinal lymph nodes and that two of the cats showed no signs of disease at the time of diagnosis (one was detected during castration and the other on routine palpation for blood donation). The third cat was a bit neglected and had a palpable intestinal lymph node. Blood tests and lymph node biopsies were compatible with the diagnosis of FIP. All three cats were treated with PI. One cat treated for 27 months remained clinically normal, although it still had blood changes indicating subclinical disease. The second cat was treated for 10 months and looked normal with lymph node enlargement. The third cat was treated for the first 3 months, continued to lose weight, and treatment was discontinued. This cat died 11 months later at the FIP. The authors believed that these results demonstrated some therapeutic benefit of PI treatment, assuming that all cats with FIP usually die within 200 days or less. The importance of treatment in these three cats is questionable. Not only were their numbers small, but some cats with no or minimal signs of disease and lesions located in the abdominal lymph node recover spontaneously over time. In addition, only one in three cats seems to have recovered completely; one died of FIP and one had symptoms of subclinical infection at the end of treatment. The authors concluded that "further studies are needed to assess the potential of the polyprenyl immunostimulant" and only cats with a well-documented dry form of FIP will be considered for inclusion in the next study.

A follow-up study of 102 cats diagnosed with dry FIP Dr. He presented the legend in 2012 at the ACVIM forum. The results of this study were as follows: “The data of the cats suspected of being FIP were thoroughly verified and cats that met the inclusion criteria were admitted to the study. Based on previous experience, we did not see any benefit of PI in cats with the wet form of FIP and these were excluded from the study. A total of 58 cats with a diagnosis of "dry" form of FIP treated with polyprenyl immunostimulant were included in the study. We started with a total of 102 cats, but cats that died before starting PI treatment, cats that died before the week of PI treatment, and cats that did not have a follow-up assessment were excluded. The study included a wide variety of purebred and domestic shorthair cats. Cats had an ocular, neurological, and abdominal form of dry FIP, with the abdominal form being the most common. 9% cats had unclear symptoms without affecting a specific organ. Three cats lived longer than 365 days (5%), 22% cats were alive for at least 165 days. PI appears to improve the well-being of treated cats. "

Notably, 44 of the total cats included in the study were excluded because they either died before treatment, died less than one week after administration, or were not re-available / examined for follow-up evaluation. Two of the groups excluded from the study had apparently severe disease and it is highly likely that most cats unavailable for follow-up either died or did not respond to treatment and also had severe disease. Of the 58 cats with milder dry FIP that remained in the study, 9% (5/58) had indeterminate symptoms without specific organ involvement, ie the disease was not confirmed. Also including these cats, only 22% (12/58) was alive after 165 days and only 5% (3/58) of these cats was alive after 365 days.

Owners who are considering using PI therapy in their cat with FIP should carefully consider these previous findings as well as the cost of treatment. Cats with wet FIP or severe dry FIP do not respond to this treatment. Of the cats with a lighter form of dry FIP, only 5% will still be alive a year later. The only claim made by the researchers or the manufacturer is that PI treatment may prolong life in a subset of cats with milder dry FIP. Because this study did not include any placebo controls, and given the fact that a small percentage of cats with dry FIP can live without PI treatment for many months and even years, this claim should be taken with some skepticism. Based on the results presented so far, CCAH cannot recommend PI as a means of treating or even prolonging the life of cats with any form of FIP.


Polyprenyl immunostimulant as a potential treatment for cats with FIP has an interesting history that extends from Russia to the United States. The research and chemical structure of PI is based on a biological "plant extract" called Phosprenyl, which is used in Russia to treat a wide range of viral infections in many species of animals. PI may thus be of Russian origin.

Translator's note: Given the price of PI and its highly controversial effect and the need for endless "treatment", it is questionable whether it makes any sense to invest money in this apparently only supportive therapy, or rather go for real treatment with GS441524, at the end of which is really healthy cat. For me, the choice is clear.