FIP Medication for Cats: Exploring EIDD-1931 as an Alternative Treatment

Not every cat responds well to GS-441524 FIP treatment. Some show little to no progress, while others require increasingly higher dosages to show improvements. In this case, EIDD-1931 may be the best alternative to a successful and effective FIP treatment.

At MolnuFIP, we’re proud to be among the first to offer EIDD-1931—a breakthrough treatment for Feline Infectious Peritonitis (FIP) backed by published research from leading scientists in the U.S. and Europe. Originally developed as a treatment for COVID-19 in humans, EIDD-1931 has shown even greater effectiveness against the feline coronavirus that causes FIP, with success rates exceeding 90%.

What sets EIDD-1931 apart is not only its impressive results, but also its affordability. Compared to GS-441524, the traditional FIP treatment, EIDD-1931 can cost as little as 20% of the price, making it a more accessible option for pet owners without compromising on efficacy.  

This article explores the science behind EIDD-1931, how it compares to GS-441524, and what current findings say about its efficacy, safety, and recommended use.

Understanding EIDD-1931: What Is It?

EIDD-1931 is the active form of Molnupiravir (also known as EIDD-2801), an antiviral drug originally developed to treat COVID-19 in humans. 

EIDD-193 is a mutagenic antiviral. It stops FIPV replication by introducing errors (mutagenesis) during the viral replication process, thus preventing FIPV from replicating effectively.

While Molnupiravir is already approved for human use, its active compound—EIDD-1931—is still under review by veterinary authorities as a potential treatment for Feline Infectious Peritonitis (FIP), a life-threatening disease caused by a mutated feline coronavirus.

Despite ongoing studies, EIDD-1931 is already being used in real-world settings to save cats from FIP. In particular, veterinarians have found it to be a powerful alternative in cases where GS-441524 has not produced successful outcomes.

Moreover, clinical experience suggests that combining GS-441524 and EIDD-1931—when administered at the correct dosages—can help prevent the development of drug resistance, a challenge that has affected some GS-based FIP treatments in the past.

Potency and Safety: How Does EIDD-1931 Compare to Other FIP Medications for Cats?

In laboratory studies, EIDD-1931 has shown greater antiviral potency than both Molnupiravir and GS-441524. However, one limitation has so far prevented its widespread adoption by veterinarians: cytotoxicity.

Unlike GS-441524, which has demonstrated minimal to no side effects, both Molnupiravir and EIDD-1931 have exhibited cytotoxic properties in in vitro tests. As a result, EIDD-1931 is currently considered a secondary or backup option—typically used when GS-441524 is unavailable, unaffordable, or proves ineffective.

Drug	EC50 (Antiviral Potency)	Cytotoxicity at a concentration of 100 µM	Dosing Frequency
EIDD-1931	0.09 µM	2.8%	Every 12 hours
EIDD-2801	0.4 µM	3.8%	Every 12 hours
GS-441524	0.66 µM	0.0%	Every 24 hours

• Lower EC50 values indicate higher antiviral activity. EIDD-1931 is 7.3 times more potent than GS-441524 in vitro.

• GS-441524 has the best safety profile (0% cytotoxicity), making it the safest option in terms of cellular damage.

Despite its high potency, EIDD-1931 carries a mild cytotoxic risk (2.8%) and potential mutagenicity of normal, healthy cells, which suggests that it is not recommended for long-term use.

These risks are especially important to consider when treating cats with underlying liver or kidney issues. For those choosing to use EIDD-1931, we recommend limiting the treatment duration to a maximum of 60 days. Based on current data, approximately 65% of cats respond well enough to complete EIDD-based treatment within 30 days, while the majority of remaining FIP cases resolve within 60 days.

We strongly advise against extending EIDD-1931 treatment beyond 60 days due to potential cytotoxicity concerns. If FIP symptoms persist after this period, we recommend transitioning to GS-441524 to complete the course of treatment.

Why Does EIDD-1931 Require Twice-Daily Dosing?

EIDD-1931 has a short plasma half-life, approximately 1 to 1.3 hours, meaning the drug leaves the body quickly and needs to be administered every 12 hours to maintain therapeutic levels. 

By contrast, GS-441524 has a half-life of around 4 hours and is effective when given once daily.

This increased frequency may be less convenient for some cat owners and may contribute to lower compliance if cat owners are not well disciplined.

Dosage Guidelines for EIDD-1931 in Cats

Recommended dosages vary based on the form of FIP:

• Wet/Dry FIP: 2.3 mg/kg every 12 hours

• Ocular FIP: 3.5 mg/kg every 12 hours

• Neurological FIP: 4.5 mg/kg every 12 hours

Molnufip.com has created a simple treatment regimen of 1 pill every 12 hours for cat owners who want to treat FIP using EIDD-1931. Visit their website for more information. 

Maximum treatment duration is 60 days, primarily due to concerns around long-term safety. If FIP symptoms are not resolved within 60 days, transitioning to GS-441524 is advised.

Real-World Evidence: What Do the Studies Say?

In a 2022 observational study, 30 cats with suspected FIP were treated with EIDD-1931 or Molnupiravir. Most of these cats had previously failed other treatments.

• 24 out of 26 cats receiving Molnupiravir as rescue therapy achieved full remission.

• 4 out of 4 cats treated with it as first-line therapy recovered fully.

• 12 cats showed visible improvement within the first 7 days.

• Over 85% showed recovery signs within two weeks.

Treatment duration ranged from 12 to 13 weeks. Side effects were rare and primarily linked to excessively high doses. 

Even cats with severe neurological symptoms—including blindness, paralysis, or seizures—showed measurable recovery at standard dosing levels.

Benefits of EIDD-1931 as FIP Medication for Cats

• Cost-effective: Approximately 1/5  the price of GS-441524.

• High potency: Stronger in vitro antiviral action than GS-based therapies.

• Accessible: Suitable as a first-line option in resource-limited settings or as a rescue treatment when GS-441524 fails.

• No risk of resistance: Due to its mutagenic mechanism, EIDD-1931 is not expected to cause antiviral resistance.

Limitations and Safety Considerations

• Potential mutagenicity: Long-term use of EIDD-1931 may carry genetic risks, including possible links to carcinogenesis, although no such effects have been confirmed in felines.

• Mild cytotoxicity: May not be ideal for cats with compromised liver or kidney function.

• Frequent dosing: Requires administration every 12 hours, which may pose challenges for some owners.

What is the Best FIP Treatment Regimen

If the patient has no ocular or neurological symptoms and is not experiencing vomiting, diarrhea, loss of appetite, or kidney-related issues:

• Begin with EIDD-1931 for 30 days.

• Extend up to 60 days if necessary.

• If FIP symptoms are not resolved by day 60, switch to GS-441524 at 10 mg/kg daily.

If ocular or neurological symptoms are present:

• Begin with GS-441524 injections for 30 days.

• Transition to EIDD-1931 for an additional 30 days.

Conclusion

EIDD-1931 is a powerful and cost-effective treatment option for Feline Infectious Peritonitis (FIP), particularly when GS-441524 is either ineffective or financially out of reach. With strong antiviral properties, EIDD-1931 has demonstrated success in treating both early and advanced stages of FIP, making it a compelling alternative for pet owners and veterinarians seeking viable treatment solutions.

Looking for safe and reliable options?

EIDD-1931 is available through trusted sources like Molnufip.com.

Need help choosing the right treatment plan?

Our expert team is available on WhatsApp to guide you based on your cat’s condition.