Treatment of Feline Infectious Peritonitis (FIP)
The most effective treatment for Feline Infectious Peritonitis (FIP) is the nucleoside analogue GS-441524, which has shown approximately 84% long-term survival rates in cats with this previously fatal disease. 1
Understanding FIP
FIP is a fatal disease that develops when feline coronavirus (FCoV) mutates within an infected cat. This mutation transforms the relatively harmless feline enteric coronavirus (FECV) into the virulent feline infectious peritonitis virus (FIPV), which causes a devastating immune-mediated disease 2.
Clinical Presentations
FIP presents in two main forms:
- Wet/Effusive form: Characterized by polyserositis with abdominal and/or thoracic effusion
- Dry/Non-effusive form: Characterized by pyogranulomatous lesions in various organs
- Mixed forms: Many cases show elements of both presentations
Common clinical signs include:
- Persistent fever unresponsive to antibiotics
- Lethargy and weight loss
- Anorexia
- Ascites (in effusive form)
- Neurological signs (in neurological FIP)
- Ocular lesions
Treatment Protocol with GS-441524
Based on the most recent evidence, GS-441524 has emerged as the treatment of choice for FIP 1:
Dosing Regimen:
- Initial dosing:
- Standard cases: 4-6 mg/kg daily
- Neurological involvement: 8-10 mg/kg daily
- Ocular involvement: 5-8 mg/kg daily
Administration:
- Oral administration is preferred when available
- Subcutaneous injection may be used when oral formulations are unavailable
- Treatment duration: Minimum 84 days (12 weeks)
Monitoring Response:
- Clinical improvement typically begins within 24-48 hours
- Complete resolution of effusion within 1-2 weeks in wet FIP
- Resolution of fever and return of appetite within days
- Monitor complete blood count, biochemistry panel, and body weight every 2-4 weeks
Treatment Outcomes:
Recent studies show that cats achieving complete response within 30 days of starting treatment have significantly better survival rates 1. Overall survival rates of approximately 84% have been reported in cats treated with legally sourced GS-441524 or remdesivir (which metabolizes to GS-441524 in the body).
Alternative Approaches
While GS-441524 is the most effective treatment, other approaches may be considered when access is limited:
Supportive Care:
- Fluid therapy for dehydration
- Nutritional support
- Drainage of effusions as needed for comfort
- Anti-inflammatory medications to manage symptoms
Immunosuppressive Therapy:
- Corticosteroids may provide temporary symptomatic relief but do not alter the disease course
- No controlled studies have proven beneficial effects of corticosteroids 3
Important Considerations
- Early diagnosis is crucial for treatment success
- Treatment must be continued for the full recommended duration even if clinical signs resolve earlier
- Relapse occurs in approximately 10.8% of treated cats and may require extended or higher-dose therapy 1
- Neurological FIP requires higher dosing and longer treatment duration
- Side effects are generally mild, with injection site pain being most common (47.8% with subcutaneous administration) 1
Prevention
- Only one intranasal FIP vaccine is available but is considered non-core and has limited efficacy
- Early-weaning programs may help protect kittens not yet exposed to FCoV
- Reducing stress and overcrowding in multi-cat environments
Without specific antiviral treatment with GS-441524 or remdesivir, FIP is almost invariably fatal, making early diagnosis and prompt treatment essential for improving survival outcomes.