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Molnupiravir (EIDD-2801/Remedy2801) in use of cats with FIP

Updated: Oct 22, 2023

Molnupiravir, also known as EIDD-2801, is a drug that has shown promise in treating cats with Feline Infectious Peritonitis (FIP). FIP is a highly fatal viral disease of cats with no FDA-approved legal treatments, leaving many owners to turn to unlicensed antiviral drugs purchased online 11.


Molnupiravir is a nucleoside antiviral prodrug that is suitable for oral administration, with activity against severe acute respiratory syndrome coronavirus 2 (SARS‐CoV‐2) and coronavirus disease (COVID‐19)

4. It has been approved in Japan since 2021 for the treatment of people with COVID-19 4. Molnupiravir has been used as a first-line therapy for suspected FIP and as a rescue therapy to treat cats who have persistent or relapsed clinical signs of FIP after GS-441524 and/or GC376 therapy 1 2 . According to a case series, molnupiravir might be an effective and safe treatment for domestic cats with FIP at a dose of 10-20 mg/kg twice daily 4 9. The dosage of molnupiravir administered in the clinical trial was 10mg/kg PO SID (oral once per day) for non-neuro/ocular FIP and 20mg/kg PO SID for ocular and neurological cases 6.


Mechanism of action:

Molnupiravir inhibits viral reproduction by promoting widespread mutations in the replication of viral RNA by RNA-directed RNA polymerase 10. It is metabolized into a ribonucleoside analog that resembles cytidine, β-D-N4-hydroxycytidine 5′-triphosphate (also called EIDD-1931 5′-triphosphate or NHC-TP) 10. During replication, the virus's enzyme incorporates NHC-TP into newly made RNA instead of using real cytidine 10. This two-step mutagenesis mechanism probably applies to various viral polymerases and can explain the broad-spectrum antiviral activity of molnupiravir 5.


Dosage and administration in cats:

According to a case series, molnupiravir might be an effective and safe treatment for domestic cats with FIP at a dose of 10-20 mg/kg twice daily 4 9. The dosage of molnupiravir administered in the clinical trial was 10mg/kg PO SID (oral once per day) for non-neuro/ocular FIP and 20mg/kg PO SID for ocular and neurological cases 6.


Safety and side effects in cats:

There is a lack of sufficient data for the use of molnupiravir in cats with FIP 4. However, the side effects of molnupiravir do not seem to be dose-dependent and can be treated with anti-nausea medications, such as Cerenia, Ondansetron, or others 3.

Comparison to other FIP treatments:

Molnupiravir is being used as a first-line therapy for suspected FIP and as a rescue therapy to treat cats who have persistent or relapsed clinical signs of FIP after GS-441524 and/or GC376 therapy 1 2 . It is unlikely that resistance to GS-441524 will extend to Molnupiravir 3 13.

The fact that it has been found to be effective as an oral medication also makes it attractive as a solo treatment, as many cats with GS-441524 resistance have suffered from injections over very long periods 13.


Clinical trials and case series:

A case series suggests that molnupiravir might be an effective and safe treatment for domestic cats with FIP at a dose of 10-20 mg/kg twice daily

4 9.


Another study reported that molnupiravir is being used as a first-line therapy for suspected FIP and as a rescue therapy to treat cats who have persistent or relapsed clinical signs of FIP after GS-441524 and/or GC376 therapy2. The study also provides a proof of principle for the use of molnupiravir in cats and supports the need for future studies to further evaluate molnupiravir as a potentially safe and effective therapy for FIP 2.


Molnupiravir has also been shown to be extremely effective in treating FIP in cats. A study published in MDPI Open Access Journals in 2020 found that molnupiravir was effective in treating FIP in cats with both wet and dry forms of the disease of varying stages. The study found that 97% of 286 cats who received molnupiravir achieved clinical remission (read: cured) within 84 days of treatment.


And in this study published on PubMed recently in 2022 using owner-reported data of 26 cats, 24 cats were cured of FIP. As a result of this study, it was found the dosages used in the above 2020 study were too high and thus revised downwards to prevent side effects. The overwhelming majority of cats will not suffer any side effects.

  • Molnupiravir is a small molecule that is taken orally by mixing with wet food.

  • Molnupiravir is effective against a wide range of viruses, including feline coronavirus and feline infectious peritonitis.

  • Molnupiravir is generally well-tolerated by cats with most cats not experiencing any side effects.

  • Molnupiravir is not currently approved by the FDA for the treatment of FIP in cats.

  • Molnupiravir is available through a compassionate use program.

If you are considering treatment for your cat with FIP, please talk to your veterinarian about molnupiravir. This treatment may be able to help your cat live a longer and healthier life. Remedy 2801™ is available on our site at FIPremedy.com starting at $299 for a complete 84-day treatment.

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