EIDD-1931 vs Molnupiravir vs GS-441524 vs Remdesivir: Understanding FIP Treatment Options in Cats

Feline infectious peritonitis (FIP) is a serious and often rapidly progressive disease caused by a mutation of feline coronavirus. When a cat receives a suspected or confirmed FIP diagnosis, treatment decisions can feel urgent, emotional, and overwhelming.

Understanding FIP Treatment Options in Cats

In recent years, multiple antiviral medications have been used clinically as part of feline infectious peritonitis treatment, including GS-441524, remdesivir, molnupiravir, and EIDD-1931. Although these compounds are related, they are not interchangeable. They differ in how they work, how they are formulated, and how well they align with feline physiology.

Understanding these differences helps cat parents move beyond confusion and make informed, confident decisions—always in partnership with their veterinarian.

How Antiviral Drugs Work Against the FIP Virus

The virus responsible for FIP is an RNA virus. To survive and spread, it must enter a cat’s cells and continuously copy its genetic material.

Antiviral treatment for FIP works by disrupting this process:

• The virus attempts to replicate inside the cell

• Antiviral compounds interfere with replication in different ways

• Viral activity slows, allowing inflammation to reduce and the immune system to recover

These medications do not instantly eliminate the virus. Instead, they aim to control viral replication over time, which is why consistent dosing, proper duration, and veterinary monitoring are essential.

Read more: FIP Treatment Guideline

Understanding Available FIP Treatments

Several antiviral compounds have demonstrated activity against the virus associated with FIP. While often grouped together, these medications play different roles in veterinary-guided care.

GS-441524

GS-441524 is one of the most extensively studied antiviral compounds used in cats with FIP. It is a nucleoside analogue that directly inhibits viral RNA replication, preventing the virus from copying itself effectively.

GS-441524 is available in formulations adapted specifically for cats, including injectable and oral options. Because it delivers the active antiviral compound directly, dosing protocols can be adjusted based on disease form, severity, and clinical response.

Although GS-441524 is widely used internationally in veterinary-guided FIP management, it is not formally approved for veterinary use in some regions due to regulatory and patent-related restrictions. Its use should always involve professional veterinary oversight.

Molnupiravir (EIDD-2801)

Molnupiravir is an oral antiviral medication originally developed and approved for human Covid-19. It functions as a prodrug, meaning it must be converted by the body into its active form before it becomes effective.

In the body, molnupiravir is metabolized into EIDD-1931. When adapted for cats, an important consideration is that molnupiravir relies on metabolic conversion and may require higher dosing compared to delivering the active compound directly. This increases the importance of formulation quality, dosing accuracy, and veterinary supervision—especially when using products originally intended for humans.

EIDD-1931

EIDD-1931 is the active antiviral compound responsible for the effects of molnupiravir. Unlike its prodrug form, EIDD-1931 does not require metabolic conversion to become active.

Delivering EIDD-1931 directly allows antiviral activity at lower doses compared to relying on conversion from molnupiravir. This has led to the development of FIP-specific formulations designed to better align with feline physiology and long-term treatment needs.

EIDD-1931 is not approved as a standalone medication for human or veterinary use and should only be used under veterinary guidance with appropriate monitoring.

Remdesivir

Remdesivir is another antiviral medication originally approved for human use. Like molnupiravir, it is a prodrug. In this case, remdesivir is converted inside the body into GS-441524.

In veterinary medicine, remdesivir is typically administered via injection or intravenous infusion, most often in hospital or referral settings. While it can serve as a source of GS-441524, administering the active compound directly is often considered more predictable for dosing and long-term management.

Comparing Antiviral Compounds Used in FIP Treatment for Cats

Aspect	GS-441524 (FIP-specific)	EIDD-1931 (FIP-specific)	Remdesivir	Molnupiravir (human form)
Compound type	Active antiviral	Active antiviral	Prodrug → GS-441524	Prodrug → EIDD-1931
Developed for FIP cats	Yes	Yes	No	No
Requires metabolic conversion	No	No	Yes	Yes
Common administration	Injectable or oral	Oral	Injectable / IV	Oral
Typical use setting	Vet-guided home care	Vet-guided home care	Hospital / clinic	Home with strict vet oversight
Dosing alignment with cats	Feline-specific	Feline-specific	Human-adapted	Human-adapted

What Veterinarians Consider When Choosing a Treatment

Veterinarians do not select FIP treatment options based on brand names alone. Clinical decisions typically include:

• Form of FIP (wet, dry, neurological, ocular)

• Cat’s age, weight, and overall health

• Disease severity and progression

• Owner ability to administer oral or injectable medication

• Access to monitoring, bloodwork, and follow-up care

This individualized approach is essential for safe and responsible veterinary guided FIP treatment.

Is There a “Best” Treatment for All Cats?

While every FIP case must be evaluated individually, in real-world veterinary-guided care, antivirals that are specifically formulated for cats with FIP are clearly preferred.

For this reason, GS-441524 and EIDD-1931 are commonly recommended as the primary treatment options for FIP. Both compounds are administered in their active antiviral form, with formulations and dosing protocols adapted specifically for feline physiology and the known behavior of the FIP virus.

Unlike antivirals originally developed for humans—which rely on metabolic conversion inside the body—GS-441524 and EIDD-1931 are delivered directly, allowing for:

• More predictable dosing

• Clearer treatment planning

• Better alignment with long-term administration in cats

• Veterinary monitoring based on FIP-specific compounds

Because they are designed and used specifically for cats with FIP, GS-441524 and EIDD-1931 are widely used as the foundation of modern FIP treatment protocols, while other antivirals are typically reserved for specific or transitional clinical situations.

Final treatment decisions should always be made by a licensed veterinarian. However, when evaluating available options, FIP-specific antivirals represent the most direct and purpose-built approach to managing this disease in cats.

Where MolnuFIP Fits in the Treatment Landscape

MolnuFIP provides EIDD-1931–based antiviral support formulated specifically for cats with FIP and intended to be used as part of a veterinarian-guided treatment plan. Its role focuses on:

• Direct delivery of the active antiviral compound (EIDD-1931)

• Oral administration to support treatment compliance

• Use alongside diagnostic confirmation, veterinary supervision, and ongoing monitoring

MolnuFIP does not replace veterinary care and should always be used under professional guidance.

What Cat Parents Should Do After a Suspected or Confirmed FIP Diagnosis

1. Discuss available FIP treatment options for cats

2. Review dosing, administration method, and monitoring plans

3. Commit to consistent treatment and follow-up

4. Report any changes in your cat’s condition to your veterinarian

Conclusion: Clear Options, Guided by Veterinary Care

Modern antiviral therapy has changed how FIP is managed, but responsible treatment still depends on informed decision-making and professional oversight. Understanding the differences between GS-441524, remdesivir, molnupiravir, and EIDD-1931 allows cat parents to focus on FIP-specific solutions designed for cats, not adapted from human medicine.

With veterinary guidance and appropriate monitoring, treatment decisions can be made clearly, confidently, and responsibly.

The MolnuFIP team also offers a FREE educational consultation to help you understand:

• Your cat’s diagnosis

• Current veterinary approaches to FCV and FIP

• Key questions to discuss with your veterinarian

Contact MolnuFIP

Website: molnufip.com

WhatsApp: +971 58 562 4801‬

Instagram: molnufip

Facebook: MolnuFIP