ABCD updates FIP treatment guidance as antiviral use expands: full analysis

Feline infectious peritonitis treatment keeps moving from last-resort medicine toward routine clinical management, and the European Advisory Board on Cat Diseases’ latest update makes that shift explicit. Published in Viruses in April 2026, the revised guidance says the availability of effective antivirals, especially oral GS-441524, has fundamentally changed the prognosis for cats with FIP, turning a disease once associated with euthanasia into one that is now frequently treatable and often curable. (mdpi.com)

The update builds on ABCD’s original 2009 guidance and a major 2023 overhaul, but the board says new data have accumulated quickly enough to justify another revision. On the ABCD website, the FIP guidance is marked as last updated on April 26, 2025, and the long-form document describes the current version as a minor update to the 2023 guidelines, with added evidence on available antivirals, monitoring, and prognostic indicators. That framing matters: this isn’t a wholesale reversal, but it is a sign that FIP treatment protocols are still evolving in real time. (abcdcatsvets.org)

At the center of the update is GS-441524, with remdesivir positioned as an important related option because it is rapidly converted to GS-441524 in cats. The guideline reviews published case series and treatment protocols that generally use 84-day courses, with dose escalation for more difficult presentations, including ocular and neurologic FIP. It also notes that cats can show rapid clinical improvement within days to weeks of starting treatment, and that markers such as fever, appetite, effusions, and ophthalmic changes can help clinicians track response. At the same time, the board points to relapse patterns and emerging prognostic signals, including worse outlooks in some cats with severe neurologic signs, hypoglycemia, or higher bilirubin levels. (abcdcatsvets.org)

The guideline also addresses molnupiravir, but with more caution. ABCD summarizes reports of remission in some cats and notes suggested 84-day oral protocols, including higher doses for ocular or neurologic disease. Still, the document says available evidence is more limited, follow-up is shorter in some reports, and one study suggested molnupiravir should not be used as a first-line agent for FIP. Legal status is another complication, especially in Europe, where the guideline notes restrictions tied to human-use regulation. (abcdcatsvets.org)

Outside Europe, the regulatory backdrop is also changing. In the U.S., FDA said in May 2024 that it does not intend to enforce new animal drug approval requirements for GS-441524 compounded from bulk drug substance when it is prescribed by a veterinarian for a specific cat with FIP under the conditions in Guidance for Industry #256. FDA also stressed that these compounded products remain unapproved drugs and are not “legal” in the approval sense, and that as of May 10, 2024, it had not received a nomination for GS-441524 as office stock. Cornell’s Feline Health Center later highlighted the practical impact of that policy shift, noting that compounded oral GS-441524 became available in the U.S. beginning June 1, 2024, through Stokes Pharmacy in collaboration with Bova. (fda.gov)

For veterinary teams, the biggest value of the ABCD update may be operational. It gives clinicians a more structured framework for discussing prognosis, selecting among antiviral pathways, monitoring response, and counseling pet parents about cost, access, duration, and relapse risk. It also reflects a more pragmatic reality: in high-suspicion cases, the guideline says a rapid response to antivirals can itself support the diagnostic process when a cat is too unstable for extensive workups, testing is unavailable, or finances are constrained. That’s a meaningful shift from the era when FIP conversations were dominated by diagnostic uncertainty and poor outcomes. (mdpi.com)

There are still caveats. ABCD notes that treatment access remains uneven across countries, some options are not legally available everywhere, and the evidence base is still stronger for some drugs and protocols than for others. The update also flags longer-term questions, including relapse management and a reported increased incidence of large-cell lymphoma within two years after successful GS-441524 treatment in one cohort, an observation that will likely need more follow-up before clinicians know how much weight to give it. (mdpi.com)

Why it matters: For general practice and feline-focused veterinarians alike, the new guidance helps formalize what many clinics have already been experiencing: FIP is increasingly a treatable disease, but successful care depends on getting the diagnosis-or near-diagnosis-right quickly, matching protocol intensity to disease presentation, and setting realistic expectations with pet parents. Standardized guidance from a major advisory body should also help reduce variation between clinics and give veterinarians a firmer footing in conversations about compounded antivirals, especially in markets where regulation is permissive but still incomplete. (abcdcatsvets.org)

What to watch: The next phase will likely focus on tighter evidence around optimal dosing, whether some cats can be treated successfully in shorter courses, how best to manage neurologic and ocular disease, and whether regulators move beyond compounding discretion toward approved veterinary products. (abcdcatsvets.org)