1
The Efficacy and Clinical Application of Molnupiravir (EIDD 2801)
in the Treatment of Feline Infectious Peritonitis (FIP)
K. Geddes & D. Nugent, MA, HDipEd (PSD/ESL), NCCP
Molnupiravir (EIDD 2801) is a nucleoside analog prodrug that blocks viral replication (Teli et
al., 2023) which has demonstrated effectiveness in clinical studies in the treatment of FIP. While
this drug is showing promise as a frontline treatment option, it has a narrower safety margin in
terms of both the individual patient and on a population level than GS-441524 and, as a result, it
is recommended to reserve Molnupiravir primarily as a rescue therapy for cats that are
experiencing a relapse after GS-441524 treatment, or those not responding well to GS treatment,
despite receiving a sufficient dosage (Taylor et al., 2025).
According to Teli et al., (2023), “Molnupiravir is an oral ribonucleoside analog, which means it
is similar in structure to one of the building blocks of RNA, a molecule that is important for the
replication of viruses, such as SARS-CoV-2.” As a prodrug, it is converted into its active form,
N4-hydroxycytidine triphosphate (EIDD-1931 triphosphate), within the body. This active form
of the drug then targets the RNA-dependent RNA polymerase (RdRp) enzyme, crucial for viral
replication. By resembling the natural substrates of RdRp, EIDD-1931 triphosphate
competitively inhibits the enzyme, introducing errors, and thereby ultimately hindering viral
RNA replication.
This mechanism makes Molnupiravir an effective treatment for SARS-CoV-2 and other RNA
viruses (Teli et al., 2023).
Several studies have indicated that the success rates for FIP treatment with Molnupiravir range
between 77%-98% (Sase et al., 2024; Sase, 2023; Roy et al., 2022).