Comprehensive Treatment Guide for Feline Infectious Peritonitis (FIP)

Feline Infectious Peritonitis (FIP) was once considered a terminal disease. However, with the development of new antiviral drugs—particularly GS-441524—FIP is now a treatable condition for many cats.

This article presents a systematic overview of FIP treatment mechanisms, leading medications, dosing protocols, and supportive therapies. All claims are backed by international research and clinical guidelines to help both cat owners and veterinarians follow evidence-based treatment plans.

I. The Breakthrough: GS-441524 as a Game-Changer

FIP results from a mutated feline coronavirus (FCoV) that infects monocytes/macrophages, causing systemic inflammation. Traditional therapies such as antibiotics or corticosteroids fail to control viral replication. In contrast, GS-441524, an adenosine nucleoside analog, offers the following:

• Inhibits viral RNA polymerase, blocking replication【Murphy et al., 2018】

• Targets critical phases of the virus life cycle

• Significantly improves clinical symptoms and survival rates

Source: Pedersen NC et al. (2019) first reported the effectiveness of GS-441524 in cats with FIP, with a documented cure rate of over 80–85%.

II. Leading Drugs and Dosage Protocols

Currently, GS-441524 and its oral derivatives (e.g., Pronidesivir) are the most recommended treatment options:

Drug Example: NeoFipronis® (Generic Name: Pronidesivir)

• Composition: Pronidesivir (active ingredient: GS‑441524)

• Dosage form: Oral tablets

• Strength: 30 mg/tablet

Data Source: Dickinson PJ et al., Vet Journal 2020; Addie DD et al., ABCD Guidelines 2015

III. Monitoring During Treatment

During therapy, monitoring is essential to assess treatment response:

• Clinical improvement: normalized temperature, regained appetite, better activity, and weight gain

• Biochemical indicators:

  • A:G ratio ≥ 0.6

  • Normalization of AGP, FSαA, total protein

  
  

• Ultrasound: reduced abdominal/chest effusion

• Special FIP types: observe neurologic signs, seizure frequency, and vision restoration

Blood work and ultrasound re-evaluation are advised every 2–3 weeks.

IV. Supportive and Adjunct Therapies

While GS-441524 is the primary drug, adjunctive treatments improve outcomes and adherence:

V. Managing Relapse and Resistance

• A small number of cats relapse within 2 weeks post-treatment—resume therapy immediately.

• If symptoms progress despite high-dose treatment, resistance mutations (e.g., M184L) may be present.

• Consider extended courses (e.g., 105 days) or alternative strategies.

Continue observing for at least 30 days post-treatment before tapering off.

VI. Pre-Treatment Considerations

• Accurate diagnosis is essential to avoid unnecessary antiviral use in other chronic conditions

• Avoid prolonged co-use of corticosteroids

• Oral tablets are preferable to injections for long-term compliance

VII. Future Outlook

FIP therapies continue to evolve, and GS-441524-based oral formulations are now legally available in some countries:

• United States (via compounding pharmacies)

• UK/Europe (under prescription)

• China (marketed as Pronidesivir)

FIP is transitioning from a terminal illness to a manageable chronic infectious disease.

References

1. Pedersen NC, et al. Efficacy of GS-441524 for treatment of FIP. J Feline Med Surg. 2019;21(4):271–281

2. Dickinson PJ, et al. GS-441524 in cats with neurological FIP. Vet J. 2020;263:105582

3. Addie DD, et al. ABCD Guidelines on FIP. J Feline Med Surg. 2015;17(7):570–582

4. Murphy BG, et al. GS-441524 pharmacokinetics and antiviral activity. Vet Microbiol. 2018;219:226–233