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Molnupiravir Clinical Study for the treatment of FIP

Molnupiravir Clinical Study for the treatment of FIP


The goal of this clinical study is to examine the safety and efficacy of Molnupiravir for the treatment of naturally acquired feline infectious peritonitis (FIP). In this report we will present our study method, real life clinical data from our study and our conclusion as to the efficacy of Molnupiravir via oral application for the treatment of feline infectious peritonitis (FIP).

2. INTRODUCTION Resistance to GS-441524 in the treatment of feline infectious peritonitis (FIP) has been reportedly increasing in frequency across the world since 2019, especially among cats with neurological FIP.

Currently drug resistance can only be overcome in two manners: 1) by progressively increasing the dosage of GS-441524 to achieve drug levels in body fluids that exceed the level of resistance, or 2) by using another antiviral drug that utilize a different mechanism to overcome FIPV, either by itself or in combination with GS-441524. Until now, the first option has been the one most frequently chosen and has proven effective in a majority of cases. However, GS-441524 resistance can be total or so high that increasing the dosage is extremely costly for cat owners and unpleasant for the cats. In such cases, the second option has been increasingly explored by researchers. Molnupiravir is one of the most promising candidates that is commercially available as a potential alternative or supplement to GS-441524.

Molnupiravir is the isopropylester prodrug of N4-hydroxycytidine. It stops the replication of FIP virus by incorporating into the genome of RNA viruses. This leads to an accumulation of mutations known as viral error catastrophe which ultimately render the FIP virus strains harmless to cats. Beta-d-N4-hydroxycytidine, the active substance in Molnupiravir, exists in two forms as tautomers. In one form, it acts as a cytidine with a single bond between the carbon and the N-OH group. In its other form, which mimics uridine, it has an oxime with a double bond between the carbon and the N-OH group. In the presence of beta-d-N4-hydroxycytidine, viral RNA-dependent RNA polymerase reads it as uridine instead of cytidine and inserts adenosine instead of guanosine. Switching between forms causes inconsistencies during transcription, which results in numerous mutations in the viral genome and a cessation of viral replication.


The trial consists of 34 FIPV-infected cats ranging in age from 5 to 96 months. Out of the 34 cats, 21 cats (62%) are relapse cases and 12 cats are newly diagnosed with FIP. All the cats in the trial were diagnosed as having one of two forms of FIP: non-effusive (dry), effusive (wet), with 12 participants exhibiting ocular or neurological symptoms. Due to ethical factors, no placebo control group was formed.

The dosage of Molnupiravir for the clinical trial is as below:- Non neuro/ocular FIP: 10mg/kg PO SID [oral once per day]

Ocular and Neuro: 20mg/kg PO SID [oral once per day]

The trial is divided into three phases of oral treatment. The duration of each phase is 30 days. A full panel blood test is carried out for the cats at the end of every phase (30 days) of treatment. This report will summarize the results and conclude the findings of the cats after their completion of the Molnupiravir treatment.

Table 1 classified the information of the participating cats. The treatment was given at various dosages according to the weight of the cats. All cats were required to complete a pre-treatment blood test. All cats were required to carry out a blood test after 30 days of treatment to measure changes in key blood test markers.

​Cat's age

Cat's weight

Type of FIPV

Status of cat


4 years





2 years





2 years