EIDD-1931 for FIP & FCV in Cats: Frequently Asked Questions (USA)

MolnuFIP™
Apr 23
4 min read

If your cat has been diagnosed with Feline Infectious Peritonitis (FIP) or Feline Calicivirus (FCV), you may have come across EIDD-1931 as a treatment option — and wondered what it is, how it compares to GS-441524, where to buy it in the United States, and whether it actually works. This guide answers the most common questions from cat owners in the USA.

EIDD-1931 for FIP & FCV in Cats: Frequently Asked Questions (USA)

What Is EIDD-1931?

What is EIDD-1931 and how does it treat FIP in cats?

EIDD-1931 is the active antiviral metabolite of molnupiravir (EIDD-2801). While molnupiravir is a prodrug that must first be converted by the body into EIDD-1931 to exert its antiviral effect, MolnuFIP™ delivers EIDD-1931 directly — bypassing that conversion step for more precise, consistent antiviral activity.

EIDD-1931 works by inducing lethal mutagenesis in RNA viruses — including the feline coronavirus (FCoV) that mutates into the FIP virus (FIPV). By flooding the virus's RNA with errors during replication, EIDD-1931 effectively prevents the virus from producing functional copies of itself, halting viral spread and allowing the cat's immune system to recover.

Each MolnuFIP™ capsule contains 15mg of EIDD-1931, formulated specifically for feline metabolic rate and gastrointestinal absorption profile — not a modified human product. Learn more about the science on the MolnuFIP™ clinical research page.

What is EIDD-1931 used for in cat treatments?

EIDD-1931 is used to treat two major feline viral diseases:

1. Feline Infectious Peritonitis (FIP) — via MolnuFIP™, for wet and dry FIP in cats that have been stable for 2–4 weeks on GS-441524 injections, or for mild cases as monotherapy under veterinary guidance.

2. Feline Calicivirus (FCV) and stomatitis — via CaliciX™ and CaliciX™ Max, targeting viral replication in cats with oral ulcers, chronic gingivostomatitis, and FCV-related disease.

Important: EIDD-1931 is not suitable as a standalone FIP treatment for cats with neurological or ocular symptoms, significant appetite or digestive problems, or pre-existing kidney and liver disease. These cats should start with GS-441524 injections for 2–4 weeks before transitioning to EIDD-1931.

How Does EIDD-1931 Compare to GS-441524?

How does EIDD-1931 compare to GS-441524 for treating FIP in cats?

Both compounds are effective antivirals for FIP, but they work differently and suit different situations:

GS-441524:

Injectable (subcutaneous) or oral capsule
First-line standard of care for all FIP types
Recommended starting point for severe, neurological, and ocular FIP
Higher per-dose cost

EIDD-1931 (MolnuFIP™):

Oral capsule only — no injections
Published research shows up to 10× greater in-vitro antiviral potency vs. molnupiravir and 7.3× higher potencythan GS-441524 under similar test conditions
More affordable — an effective cost-reduction option especially for the maintenance phase
Ideal as a step-down from GS-441524 once the cat is stable, or for mild FIP cases under veterinary guidance
Also active against FCV (GS-441524 is not)

For many cat owners in the USA, a combined approach works well: start with GS-441524 injectables for 2–4 weeks to stabilise the cat, then transition to MolnuFIP™ oral capsules for the remainder of the 84-day protocol. This reduces treatment cost significantly without compromising outcomes. Read the full comparison on the MolnuFIP™ blog.

Where to Buy in the USA

Where can I buy EIDD-1931 antiviral treatment for cats with FIP in the United States?

MolnuFIP™ (molnufip.com ) ships directly to the United States. Orders are processed and dispatched within 24 hours in tamper-evident, discreet packaging. MolnuFIP™ operates local warehouses to support fast and reliable delivery across North America.

Available products:

MolnuFIP™ — EIDD-1931 15mg capsules for FIP treatment (€39)
CaliciX™ — EIDD-1931 for FCV/stomatitis (€39)
CaliciX™ Max — High-potency 30mg EIDD-1931 for severe FCV (€69)

Where to buy MolnuFIP online in the USA with fast shipping?

Order directly at molnufip.com. All orders are dispatched within 24 hours. For questions about delivery timelines to your specific state, visit the shipping policy page or contact the team at hello@molnufip.com.

What is the most affordable FIP treatment available online in the US?

MolnuFIP™ is positioned as one of the most cost-effective EIDD-1931 treatments available to US cat owners. At €39 per pack, combined with the option to transition from GS-441524 mid-protocol, MolnuFIP™ can significantly reduce the total cost of an 84-day FIP treatment course without compromising antiviral coverage. See the full cost comparison on the MolnuFIP™ blog.

Effectiveness & Safety

How effective is oral antiviral treatment for Feline Infectious Peritonitis?

EIDD-1931-based treatment for FIP has demonstrated strong efficacy in clinical and field settings. A field study evaluating 46 cats on a dual GS-441524 + EIDD-1931 protocol achieved a 78.3% remission rate even in previously relapsed cats, with a relapse rate of just 6.5%. For cats on MolnuFIP™ as part of a step-down or combination protocol, clinical outcomes are consistently positive when the FIP treatment guideline is followed correctly.

What are the benefits of soft gel capsules for cat antiviral medication?

MolnuFIP™ is delivered in soft gel capsules — a format designed for ease of home administration. Key advantages:

No injections — stress-free for both cat and owner
Twice-daily dosing (12 hours apart) — maintains stable blood levels
Consistent dose delivery — removes variability of injectable administration
Suitable for long-term use — particularly for the maintenance phase of FIP treatment or ongoing FCV management

How to order cat antiviral capsules with veterinary guidance in the USA?

Visit molnufip.com and review the FIP Treatment Guideline or FCV Treatment Guideline before ordering. The MolnuFIP™ support team is available to assist with treatment-related questions — contact via the contact page or email hello@molnufip.com. Veterinary resources are also available on the vet resources page for practitioners looking to review the clinical evidence.

Still Have Questions?

MolnuFIP™ supplies EIDD-1931 antiviral capsules for the treatment of Feline Infectious Peritonitis (FIP) and Feline Calicivirus (FCV) in cats across the United States and worldwide.