Step up your practice: Start treating FIP today

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For years, a treatment for feline infectious peritonitis (FIP) has been talked about as a hypothetical, a what-if, but now it is a reality. US veterinarians can treat this fatal disease with GS-441524, along with current antivirals such as remdesivir, Paxlovid, and others.

What is FIP

FIP is a historically fatal-without-treatment disease that stems from a feline coronavirus, an RNA virus. Although the majority of affected cats are diagnosed before they are 2 years old, it is important for clinicians to be aware that cats of any age and breed can get it. FIP can present in multiple ways, and current suggested treatment protocols have high rates of survival in treating the following:

• Effusive (wet) FIP: protein-rich effusions in the abdomen and chest cavity
• Non-effusive (dry) FIP: pyogranulomatous mass lesions on any organ, such as intestines, kidneys, eyes, etc
• Neurological FIP: brain or spinal cord deficits seen through seizures, walking abnormally, trembling, etc
• Ocular FIP: cloudy or bloody eyes, different pupil sizes, and/or cats showing pain by holding their eyes closed

Life-saving treatment is now available in the US

Sally Coggins, BVSc, MANZCVS, PhD candidate at the University of Sydney, in Australia, recommends GS-441524, an antiviral tablet now available in the US through Stokes Pharmacy, to treat FIP. The FDA allows compounding GS-441524 from a bulk active pharmaceutical ingredient under the FDA Center for Veterinary Medicine’s Guidance for Industry #256’s enforcement discretion. While GS-441524 is under review for approval as office stock, it can be ordered and kept as office stock in most states.

Clinical studies in Australia and the UK have shown a greater than 80% survival rate when treating FIP with Bova GS-441524. Specifically, results from a study at the University of Sydney showed a 96% survival rate if a cat lives through the first 48 hours of treatment and an 86% survival rate to 6 months after treatment.¹ Bova GS-441524 has been used in multiple clinical research studies around the globe.^1,2,3

The availability of this life-changing drug is groundbreaking news in the US. Previously, with veterinarians unable to prescribe or advise on the use of GS-441524, the use of unregulated black market FIP drugs grew among pet owners. Although there has been some success using black market drugs,⁴ this practice lacks veterinary oversight and quality control, which leads to a great variation in potency and no clear instructions for use.⁵ These problems are solved with the Bova formulation of GS-441524.

The dosage of GS-441524 depends on the type of FIP, the cat’s weight (Table 1), and clinical responses. A minimum of 84 days of total treatment is recommended in all cases.

Researchers and FIP experts recommend the following:

• The daily dosage of oral GS-441524 can be given once daily or divided twice daily; some cats may benefit from twice-daily treatment to optimize serum levels of GS-441524.
• Once-daily treatment is acceptable for cats that are challenging to medicate and/ or obtain a positive response.
• Higher dosages may overcome issues with poor absorption in some cats; the drug may better cross the blood-brain barrier and the blood-eye barrier.
• The dosage should be adjusted according to clinical responses.

The introduction of Bova GS-441524 tablets led to most treatment regimens starting with tablets from the first day, resulting in a better-tolerated treatment compared with previous options.

“From a welfare perspective, being able to move these cats over to oral therapy is so important, and to be able to just bypass injectables altogether in cats that have a competent swallow reflex has been a real advantage,” said Coggins.

Bova GS-441524 should be given on an empty stomach. Coggins recommends food be withheld for at least 1 to 2 hours before each dose, but the fasting must be tailored to the age of the cat. While further study is needed on the effect of food on absorption, a tablespoon of wet food or a creamy treat can be used to wash it down. A full meal must be given at least 30 minutes later.

While starting this treatment, practitioners should support owners who will need to administer the tablet at home. Coaching owners to administer at-home treatment and perform weight and symptom monitoring is important since the treatment lasts 84 days. Empowering owners to use positive reinforcements, like creamy treats, with their cats ensures the GS-441524 treatment’s success.

While previous research suggested injectable remdesivir be used first in FIP cases and then be transitioned to oral medication, current studies with the Bova formulation show that FIP cats can be treated successfully when starting with Bova GS-441524 tablets. In the US, remdesivir treatment for cats can only be used off-label with Veklury, a medication used to treat humans with COVID-19. It is acceptable to use off-label on cats, with the main barrier being that it is difficult to obtain because it is generally used to treat humans in hospitals.

When treating with Bova GS-441524, it is especially important to monitor the cat’s clinical response during the first 6 weeks of treatment. A weekly physical exam or a home weight check, if the owner has a digital baby scale, is recommended. Cats typically gain weight rapidly, and the dose needs to be recalculated regularly to ensure they are being maintained at the desired dose rate. Always round up to the nearest one-fourth tablet so cats are growing into the dose, not out of it. Although monthly blood tests are considered appropriate, a focus on clinical response during the first half of treatment is very important. If clinical signs resolve rapidly, the cat is eating and playful again, and their fever has resolved, serum biochemistry and hematology can be assessed at 6 to 8 weeks and again at 10 to 12 weeks before determining whether to stop treatment. In studies, mild persistent hyperglobulinemia and abdominal lymphadenomegaly are sometimes reported, but this does not indicate a relapse.

For successful treatment with Bova GS-441524, follow these guidelines:

• Do not allow cats to get less than a daily 15mg/kg dose at any point.
• Do not adjust the dosage down with weight drops; the dose should only go up with weight gains.
• Do not stop treatment before the 12 weeks, even if the cat is responding well and quickly. There is currently not enough data supporting shorter treatments.
• Do not continue any type of corticosteroids beyond the first 1 to 2 weeks.

If there is a need to troubleshoot any suboptimal responses to these treatments, take the following steps:

• Ask, “Was the diagnosis definitively FIP?”
• If the answer is yes, increase the dosage by 5 to 10 mg/kg daily and try the strategy of dividing the dose every 12 hours.
• Consider adding Paxlovid, which is legal for off-label use via prescription in the US, or switching to an alternate antiviral such as EIDD-1931 or molnupiravir
• Mefloquine can also be used with GS-441524, but it has been found to be a much weaker antiviral for treating FIP and is considered a last resort

Lastly, throughout this treatment, be sure to provide supportive care. Cats with FIP may be in pain from pleural and peritoneal inflammation, distension from masses, uveitis, and neurological lesions. Consider an analgesic that is appropriate for that patient. Furthermore, they could need fluid therapy, nutrition support, antiemetics, specific ocular/neurological medications, or more. However, be aware that no specific supplements have been studied to be used alongside the antivirals mentioned. Most cats that respond well do not require supportive measures beyond the first week of therapy.

There are many variants in treating FIP. But with the introduction of regulated GS-441524, veterinarians can now provide ethical, critical support to their patients, improving the chance of survival for thousands of cats in the US.

References

1. Coggins SJ, Norris JM, Malik R, et al. Outcomes of treatment of cats with feline infectious peritonitis using parenterally administered remdesivir, with or without transition to orally administered GS-441524. J Vet Intern Med. 2023;37(5):1772-1783. doi:10.1111/jvim.16803
2. Taylor SS, Coggins S, Barker EN, et al. Retrospective study and outcome of 307 cats with feline infectious peritonitis treated with legally sourced veterinary compounded preparations of remdesivir and GS-441524 (2020–2022). J Feline Med Surg. 2023;25(9):1098612X231194460. doi:10.1177/1098612X231194460
3. Green J, Syme H, Tayler S. Thirty-two cats with effusive or non-effusive feline infectious peritonitis treated with a combination of remdesivir and GS-441524. J Vet Intern Med. 2023;37(5):1784-1793. doi:10.1111/jvim.16804
4. Jones S, Novicoff W, Nadeau J, Evans S. Unlicensed GS-441524- like antiviral therapy can be effective for at-home treatment of feline infectious peritonitis. Animals (Basel). 2021; 11(8):2257.
5. Kent AM, Guan S, Jacque N, Novicoff W, Evans SJM. Unlicensed antiviral products used for the at-home treatment of feline infectious peritonitis contain GS-441524 at significantly different amounts than advertised. J Am Vet Med Assoc. 2024;262(4):489-497. doi:10.2460/ javma.23.08.0466

McVey is the pharmacist-in-charge and coowner of Stokes Pharmacy. McVey holds a pharmacy degree from Temple University School of Pharmacy in Philadelphia, Pennsylvania, and has over 35 years of experience. McVey is also a licensed consultant pharmacist, offering expert advice on medication therapy management, regulatory compliance, and patient care optimization.