Polyprenyl Immunostimulant™ product information

What is Polyprenyl Immunostimulant™?
Polyprenyl Immunostimulant™ is manufactured by Sass & Sass, Inc. and is the first and only product used as a therapeutic for signs associated with feline rhinotracheitis, a disease caused by herpesvirus. The U.S. Department of Agriculture granted the conditional license for Polyprenyl Immunostimulant™ following acceptance of data supporting the product efficacy, safety, and purity. Sass & Sass, Inc. continues to perform additional studies on the product potency.

Polyprenyl Immunostimulant™ is the only therapeutic approved by the USDA for the treatment of feline rhinotracheitis. It reduces the severity of the disease in cats. It is a very safe, well-tolerated oral liquid designed with cats in mind. It was safe in 390 cats in the field study and caused no adverse events in a four-digit number of cats and kittens treated over nearly eight years after its licensing. Our user surveys show Polyprenyl Immunostimulant™ makes cats happy, energetic, and returns felines to their healthy selves. Polyprenyl Immunostimulant™ is formulated as a 2 mg/mL solution of phosphorylated polyprenols and is offered in 10 mL vials or packs of 6 x 10 mL vials.



The only USDA-approved oral treatment for feline rhinotracheitis. No analogs or similars exist.


Developed, sourced, and manufactured 100% in the USA.


No adverse events during the studies and seven years post-market.


Easy to administer a small volume liquid to cats.

What does Polyprenyl Immunostimulant™ do?
Polyprenyl Immunostimulant™ aids in the reduction of clinical signs resulting from Feline Rhinotracheitis Virus infections in cats eight weeks of age or older.

Many veterinary specialists agree that immunomodulation is imperative in viral diseases that cause massive damage to immunity. Most viral infections start and end with immunity. A viral disease begins with the virus evading the weakened immunity of an immuno-compromised cat and ends when the restored immunity controls or suppresses the virus.

Herpesvirus, the virus responsible for Rhinotracheitis (FVR), causes a latent infection with periodic flareups. It cannot be cured; it can only be controlled so that the cat does not experience URI (Upper Respiratory Infection) signs that make the feline feel bad. A correct immune response keeps the virus in check and does not allow it to replicate uncontrollably and kill cells.

All herpesviruses destroy the correct immune response in order to survive and proliferate, and the feeling of being diseased comes from the lack of the proper immune response. Antivirals fail to prevent relapses because they do not address the true reasons why cats develop viral diseases: genetic immunodeficiency and the suppression of immunity in the multiple cats’ environment – such as shelters or multiple cats households.

Antivirals may temporarily reduce the viral load during flare-ups when the virus destroys the cells and gets released in large numbers. But the cats do not read the viral titer report. If immunity has been suppressed, cats feel equally bad regardless of the viral loads (Cameron et al, 2006, J.Infect.Disease, 193:664-671.)<

Polyprenyl Immunostimulant™ signals the cat’s own cells to mount back the correct immunity, reduces the clinical signs, and alleviates the feeling of sickness by restoring proper immune response. 

Polyprenyl Immunostimulant™ is a very safe product.
A field safety study was conducted in 390 owned cats in 10 states. The oral application of 0.5 mg/kg Polyprenyl Immunostimulant™ twice daily for 15 days was safe for cats at or above eight weeks of age. Fewer than 2% of cats may dislike the taste or develop diarrhea. Read about the study here.

Clinical trials to establish efficacy of Polyprenyl Immunostimulant™:
Twenty 6 to 10 week old, specific pathogen-free cats of both sexes enrolled into placebo-controlled, randomized, double-blinded virus challenge study. The cats were challenged with feline rhinotracheitis virus. Ten randomly selected animals (experimental group) received 0.5mg/kg of Polyprenyl Immunostimulant™ orally twice daily on days 0 through 14 days post-challenge (DPC); other ten cats (placebo group) received an equal amount of placebo solution.
The cats were examined for clinical signs daily for 21 DPC, and clinical scores were recorded daily. All cats enrolled in the study tolerated the administration well, no adverse effects were noted. No toxicity was observed with the substance. Animals (placebo group) had the signs persist for 8-11 days with one animal having very mild signs over the course of the study (21 days).
All cats in the study developed signs of rhinotracheitis at some time of the experiment. Distributions of clinical scores for different signs were initially analyzed for normality, and the normal distributions were then compared using an unpaired Student t-test.
Persistence of the disease signs in the experimental group (treated with Polyprenyl Immunostimulant™) did not exceed 7 days when, whereas 5 of 10 untreated animals (placebo group) had the signs persist for 8-11 days with one animal having very mild signs over the course of the study (21 day).
The complete results of the clinical trials are published here.  

Additional information

What is the dose I need for my pet?
The best way to determine the dose is to ask your veterinarian. If your cat has rhinotracheitis (herpes), you need to use the dose as indicated on the label: 0.5 mg/kg twice daily for 15 days. However, veterinarians may prescribe different doses or use PI in other diseases, for other indications. Your veterinarian will always remain the best source of information. Dr. Alfred Legendre of the University of Tennessee has several published papers describing his clinical research with Polyprenyl Immunostimulant™.

How is Polyprenyl Immunostimulant™ administered?
Polyprenyl Immunostimulant™ has been formulated for oral administration. However, your veterinarian may order a different route.

Is Polyprenyl Immunostimulant™ safe? 
Yes. You may check more data by clicking here. Safety of Polyprenyl Immunostimulant™ has been tested in 390 cats in 10 states and used for disease control in close to 800 cats, several dozen ferrets, dogs, birds, and mice. No adverse events were reported.

My cat hates taking PI. Is there anything I can do, such as adding PI to his favorite food? 
Most cats will object to taking any medication, or rather anything forced on them against their will. You need to work on your techniques of medication your cat with your veterinarian. PI is tasteless but its smell is recognized as offensive by some cats (albeit we know of two unrelated cats who craved PI). Masking the smell helps the process. Many cats agree taking PI in tuna juice. PI is unstable in tuna juice, so you need to get your cat lap it up immediately after mixing.

What if I start my cat on PI and later on it turns out that he/she does not have the disease? 
Polyprenyl Immunostimulant™ is safe and it upregulates innate immunity regardless of the presence of the disease. Your cat will have no problems from the administration of PI. Healthy cats on our safety studies remained healthy.

Can Polyprenyl Immunostimulant™ be combined with other drugs?
You need to ask your veterinarian. Published research by Dr. Alfred Legendre provides information on the use of concurrent drugs.

I think my pet has an adverse response. What do I need to do?
You need to see your veterinarian immediately. If the veterinarian confirms that the adverse event is due to the medication and not to the progression of the disease, you need to file a report with the manufacturer Sass & Sass.

If you are a veterinarian:
You need to get to our order page and select an appropriate choice. If you are a veterinarian, you will need to register to get a complete package of information. Veterinarians may place orders without registering too, by downloading our US order form for US veterinarians or our international order form for non-US veterinarians, completing it and sending to us by e-mail orders@vetimmune.com or fax (1-865-940-0042).

If you are not a veterinarian:
If you are a cat guardian, you need to download the Package Insert and our US order form for US patients or our international order form for non-US patients and take those to your veterinarian. 
If you have any questions, please e-mail or call us at 1-209-600-7070.

May a veterinarian place an order and let the patient pay for it?
Yes. The order form provides that option. Veterinarians need to fill out the account information and order information sections and let patients complete the shipping information and payment information sections.

My veterinarian has not heard about PI. What information do I need to give him/her?
The best source of information for your veterinarian will be Veterinary Information Network (VIN) to which your veterinarian has an access through professional channels. You may download our package insert and research publications and take to your veterinarian along with the order form.

Do you require prescriptions? Can you fill a prescription?
No. We need to have an order form completed by veterinarians. We are not a pharmacy and cannot fill prescriptions. Veterinarians need to dispense Polyprenyl Immunostimulant.

How do I order a refill?
Veterinarians need to indicate, in order information section of the order form, if they authorize refills using the same form or send in a separate form with every reorder.

What is the cost of the treatment?
You need to work this out with your veterinarian because the cost to you depends on many factors, including the weight of your pet, dose, and frequency of administration.  Some practices may also charge fees. The final cost to you will also depend on the cost of shipping by FedEx. The dose and frequency can be decided by a veterinarian only. In our experience, the cost to owners varies greatly depending on so many factors.

Do you know veterinarians in my area who have used PI?
Most likely, yes. We have worked with many veterinarians and have a locator of veterinarians who have experience with PI. You can find the information by clicking here.

Who distributes Polyprenyl Immunostimulant™ in the US or overseas?
Polyprenyl Immunostimulant™ is distributed by VetImmune® and by Panda Plus s.r.o. in Czechia.

How do I store Polyprenyl Immunostimulant™? 
Polyprenyl Immunostimulant should be kept refrigerated (not frozen) or stored in the dark at 12-30°C (54-86°C).

How long is Polyprenyl Immunostimulant™ good for? 
Polyprenyl Immunostimulant™ is stable for at least 18 months. Please check the expiration date on the label.

How soon will you ship my order? 
We are doing our best to ship all orders on the day they are received. However, we have cutoff times due to local pickup schedules. We will be able to ship on the same day if we have your complete order by:
3 PM ET if you requested shipping by FedEx Ground
5 PM ET if you requested shipping by FedEx Express or FedEx International services 

We do not ship on Saturdays or Sundays or on major public holidays. All orders received after cutoff on days off will be processed on the next business day.

Are you shipping by UPS? DHL? USPS? 
No, we use FedEx only.

What is the cost of shipping? 
The cost of shipping depends on the service you select. FedEx allow making easy estimated using their calculator at www.FedEx.com. Here’s what the information you need to calculate the cost:
Weight – 1 lb for 1-2 packs of 6 vials
Packaging – FedEx Pak or FedEx Box for Express service, our own packaging for FedEx Ground. FedEx Ground shipping services are available to US customers during the warm seasons only. FedEx Ground may be available to our Canadian customers.
Shipping from zip code 37830
Added: pickup, insurance for the full value, signature confirmation

Does the package need to be refrigerated? 
No. Polyprenyl Immunostimulant™ is stable at temperatures above freezing and does not need to be refrigerated during transit.

It is very hot where I live. Would Polyprenyl Immunostimulant™ get spoiled if the package is left outside until I pick it up?
No. Polyprenyl Immunostimulant™ is stable at temperatures above freezing and would not spoil even at elevated temperatures during transit. However, we would not recommend leaving it outside for prolonged periods of time.

It is very cold where I live. Would Polyprenyl Immunostimulant™ get spoiled if the package is left outside until I pick it up? 
Very likely it will. Polyprenyl Immunostimulant™ is unstable at lower temperatures – it should never be frozen therefore. In some areas, we will not allow signature waivers in the winter time to ensure that the product does not get degraded waiting outside. Freezing breaks fine micelles in the solution, and Polyprenyl Immunostimulant™ may precipitate. It will remain safe but its delivery to the organs will be affected.

May a veterinarian place an order and let the patient pay for it?
Yes. The order form provides that option. Veterinarians need to fill out the account information and order information sections and let patients complete the shipping information and payment information sections..

What type of payments do you accept?
We accept all major credit cards, Paypal, and wire transfers. Orders of $1000 or more require a Credit Card Authorization form to be submitted. Orders of $2500 or more require a wire transfer or equivalent.

Do you accept CareCredit?
No. Care Credit does not allow payments for medicines.

May I return unused Polyprenyl Immunostimulant™?
Sorry, we cannot accept returns.

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