FIP Treatment update – August 2025

Through the course of understanding and treating FIP there has been a lot learning. As we near the end of 2025 a lot has been learned over the past year. Bova has published an update on treatment FIP. A summary of this publication is below with a link to read more.

Antiviral Treatments
First-Line Therapy: Nucleoside analogues like GS-441524 (oral or injectable) and remdesivir are the preferred treatments. Oral GS-441524 is effective from the start of treatment and is less painful than injectable remdesivir.
Second-Line Therapy: Molnupiravir (EIDD-2801) and its active form EIDD-1931 are used for cats that fail to respond to GS-441524 or remdesivir. These drugs have a narrower therapeutic window and more side effects.
Adjunctive/Last-Resort Options: Protease inhibitors like nirmatrelvir (Paxlovid™) and GC-376 are less commonly used and reserved for refractory cases.
Dosage: Treatment duration is typically 6-12 weeks, with dosages adjusted based on the type of FIP (effusive, neurological, or ocular) and the cat’s response.

Monitoring and Adjustments
Cats should be weighed weekly to adjust dosages as they gain weight during recovery.
Clinical improvements (e.g., appetite, resolution of effusions) are expected within 2-5 days, with effusions resolving by 2 weeks.
Persistent abnormalities like mild hyperglobulinemia or lymphadenopathy at the end of treatment are not necessarily indicative of relapse.

Side Effects
Common side effects include injection pain (remdesivir), mild ALT enzyme increases, and occasional cytopenias (molnupiravir/EIDD-1931).
Side effects resolve upon stopping the medication.

Relapse Management
Relapse during or after treatment may require dosage increases, switching antivirals, or extending treatment duration.

Supportive Care
Nutrition is critical; appetite stimulants and feeding tubes may be needed.
Analgesics, antiemetics, and corticosteroids (in specific cases) can be used to manage symptoms.

Prognosis
Response rates exceed 85%, with survival rates often over 90%. Relapse is rare (<10%) and typically occurs within the first month after treatment. Additional Considerations
Neutering, vaccination, and parasite prevention are safe during or after treatment.
Antiviral treatment trials can aid in diagnosis when definitive testing is unavailable.
Immunostimulants and mefloquine are not recommended due to limited evidence of efficacy.

Precautions
Avoid black-market antivirals due to quality concerns.
Do not treat in-contact cats without confirmed FIP, as FIP is not directly contagious.

Future Directions
Research continues to refine treatment protocols, monitor antiviral resistance, and explore therapeutic drug monitoring (TDM) for dose optimization.

You can check our posts about FIP to learn more