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GS-441524 vs. Molnupiravir: Choosing the Right FIP Treatment for Your Cat

2 cat wearing a doctor suit hugging each other

Besides supportive care, antiviral medications are now used to treat Feline Infectious Peritonitis (FIP). There are two main types of antivirals available: GS-441524, which has been in use since 2019, and Molnupiravir, a newer option introduced in 2023. Both GS-441524 and Molnupiravir are available in injectable and capsule forms. Here's a comparison of the two medications to help you make an informed decision:


  • Mechanism of Action: GS-441524 is a nucleotide analog with phosphate, which works by inhibiting viral replication. This mechanism is effective against all forms of FIP, including wet, dry, neurological, and ocular.

  • Administration: GS-441524 is administered subcutaneously (under the skin), either through injections or via saline solution, leading to better absorption than oral medications.

  • Side Effects: The main side effects are injection site reactions (which resolve after treatment) and potential mild liver impact.


  • Mechanism of Action: Molnupiravir is a ribonucleoside analog (without phosphate) that also disrupts viral replication. It is effective in the early stages of FIP and some cases of wet FIP, but its efficacy in dry FIP is less established.

  • Administration: Molnupiravir is typically administered orally in capsule form.

  • Side Effects: Common side effects include diarrhea, vomiting, and loss of appetite.





Injection and Pill


Side effects

  • Injection side reactions

  • Mild liver impact

  • Mild liver impact

  • Bone marrow


  • Cover all ranges of FIP forms

  • High Success Rate up to 97%

  • Suitable for Wet Form or Begining stage of Disease

  • Not Suitable for Dry form especially Neuro or Ocular

  • Cure rate unconfirmed

  • Not have long term result from any research


More Expensive Than Monulpiravir

Cheaper or Equal in some country


For injections, it may be necessary to have a veterinarian administer them if you are unable to do so yourself (injections are given once a day)

If your cat is difficult to medicate, it may be necessary to have a veterinarian or assistant administer the medication, and it will need to be given twice a day.

Treatment Duration

at least 84 days

at least 84 days(Unconfirmed)

Trestment response

With in 1 Week

Between 2 - 4 Weeks

Which Treatment is Right for Your Cat?

The choice between GS-441524 and Molnupiravir depends on various factors, including:

  • FIP Form: GS-441524 is effective against all forms of FIP, while Molnupiravir is primarily used for early-stage and wet FIP.

  • Severity of Symptoms: GS-441524 is often preferred for more severe cases due to its proven track record and better absorption.

  • Administration Preference: If you prefer oral medication, Molnupiravir might be an option, but be aware of its potential side effects and limited efficacy in certain FIP forms.

Consult your veterinarian to discuss the best treatment option for your cat's specific needs and circumstances. They can assess your cat's condition, weigh the pros and cons of each medication, and create a personalized treatment plan.

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