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Treatment of 18 cats with FIP with molnupiravir: A case series

Flood Article: Molnupiravir treatment of 18 cats with feline infectious peritonitis: A case series
Okihiro Sase

Table of Content to hide
Abstract
1. Introduction
2 MATERIALS AND METHODS
2.1 Cats
2.2 Preparation of the medicine
2.3 Treatment
2.4 Measurements
2.5 Adverse Events
2.6 Statistical analysis
2.7 Ethics
3 RESULTS
3.1 Characteristics of the disease and treatment
3.2 Outputs
3.3 Security
4 DISCUSSION
Additional information
References

Abstract

Basic information
Feline infectious peritonitis (FIP) is a viral disease of cats caused by certain strains of the coronavirus that has a high mortality rate.

The goal
This case series reports the results of treatment of cats with FIP with molnupiravir.

The animals
Eighteen cats diagnosed with FIP at You-Me Animal Clinic, Sakura-shi, Japan between January and August 2022 and whose owners gave informed consent for this experimental treatment.

Methods
In this prospective observational study, molnupiravir tablets were prepared directly at the You-Me Animal Clinic. Owners administered 10-20 mg/kg PO twice daily. The standard duration of treatment was 84 days.

The results
Of the 18 cats, 13 cats had effusive FIP and 5 cats had non-effusive FIP. Three cats had neurological or ocular signs of FIP before treatment. Four cats, all with effusive FIP, died or were euthanized within 7 days of starting treatment. The remaining 14 cats completed treatment and were in remission at the time of writing (139-206 days after initiation of treatment). Elevated serum alanine transaminase (ALT) activity was found in 3 cats, all on days 7–9, and all recovered without intervention. Two cats with jaundice were hospitalized, 1 during treatment (day 37) and 1 with severe anemia at the start of treatment.

Conclusions and clinical significance
This case series suggests that molnupiravir may be an effective and safe treatment for domestic cats with FIP at a dose of 10–20 mg/kg twice daily.

1. Introduction

Feline infectious peritonitis (FIP) is a viral infectious disease occurring mainly in domesticated cats.1, 2 FIP is an aberrant immune response to infection with feline coronavirus (FCoV), which is ubiquitous, especially in breeding and rescue breeds, usually with no or mild clinical signs. Fecal-oral transmission of FCoV often occurs, especially in environments with multiple cats3 and the incidence of FIP in cats exposed to FCoV is up to 14 %.4, 5

Feline infectious peritonitis is usually classified as either effusive or non-effusive based on clinical presentation.1, 6, 7 Until the development of specific antiviral therapy, the case fatality rate associated with FIP was high, and most affected cats died within weeks to months of the onset of clinical signs.

Some nucleoside analogs, including remdesivir (GS-5734) and its active metabolite GS-4415248, inhibit viral RNA synthesis and have high antiviral activity against FCoV causing FIP in cats.9, 10 Despite the expectations of veterinarians and cat owners, the developer decided not to apply for approval of GS-441524 for the treatment of FIP. As a result, many cats with FIP are being treated with the unapproved drug GS-441524, and concerns have been raised about the quality, purity, and efficacy of the unapproved products available on the world market. Mutian has excellent efficacy and safety.11-14 Although the manufacturer did not disclose the chemical structure of the active substance and its exact concentration, its active substance is GS-441524.12

Molnupiravir is an oral nucleoside antiviral prodrug with activity against severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) and coronavirus disease (COVID-19). As of 2021, molnupiravir is approved in Japan to treat people with COVID-19. There are published reports on the efficacy and safety of molnupiravir in cats15 , but sufficient data on the use of molnupiravir in cats with FIP are lacking. Due to the lack of treatment options for FIP, we began offering molnupiravir to clients at our clinic, using small tablets prepared in-house for easy administration to cats. Here we present the results of the first 18 cats that underwent this FIP treatment in our clinic.

2 MATERIALS AND METHODS

2.1 Cats

All cats attending the You-Me Animal Clinic in Sakura-shi, Japan since January 2022 diagnosed with FIP and whose owners provided informed consent were included in this case series. Feline infectious peritonitis was diagnosed based on a combination of clinical signs (decreased appetite, enlarged abdominal lymph nodes, weight loss, fever, effusions, or uveitis) and laboratory test results for anemia and hyperglobulinemia, including the albumin-to-globulin (A/G) ratio and values of α1-acid glycoprotein (AGP). The presumptive diagnosis of FIP was based on the identification of FCoV RNA in samples from abdominal or pleural effusion (effusive FIP) or whole blood (non-effusive FIP), or from fine needle aspiration (FNA) of pyogranulomatous lesions. Virus detection was performed by reverse transcription polymerase chain reaction (RT-PCR) in the following testing laboratories: abdominal effusion and FNA samples at IDEXX, Japan (using a LightCycler 480 System II, Roche Diagnostics KK, Basel, Switzerland) and whole blood at Canine Lab., Japan (using CFX Connect, Bio-Rad Laboratories, Inc, Irvine, CA, USA). Abdominal or pleural effusion samples (1 ml each) were taken by ultrasound-guided abdominocentesis, respectively. by thoracentesis and were evaluated for the total number of nucleated cells, protein content, A/G ratio and cytology. Whole blood samples (1 ml) were collected and sent in ethylenediaminetetraacetic acid (EDTA) tubes.

2.2 Preparation of the medicine

Tablets containing molnupiravir 20 mg were prepared at the You-Me Animal Clinic. Briefly, molnupiravir powder was extracted from 20 commercially produced molnupiravir 200 mg capsules (MOVFORE, Lot No. HH2201001 [HETERO HEALTHCARE, Hyderabad, India]) and mixed with powdered cellulose (microcrystalline cellulose powder, NICHIGA, Takasaki, Japan) using a mortar and pestle (Matsuyoshi Medical Instruments Co, Ltd, Tokyo, Japan) to make a total of 12 g of powder mixture. The powder was shaped into approximately 200 6 mm wide sectional scored tablets using a generic tablet press made in China.

2.3 Treatment

Treatment with molnupiravir was initiated when FIP was highly suspected on the basis of clinical presentation or when FCoV RNA was detected by PCR; this date was marked as the first check. The following dosages were chosen: 20 mg/kg/d (10 mg/kg twice daily) for cats with effusive type, 30 mg/kg/d (15 mg/kg twice daily) for cats with non-effusive type and cats with pyogranulomatous lesions, and 40 mg/kg/d (20 mg/kg twice daily) for cats with neurological or ocular signs of FIP. Dosage may be increased or decreased in animals showing clinical deterioration or adverse reactions. Dosage was chosen based on estimated animal dosages listed on the Internet16, 17 and based on the adult human COVID-19 dose of molnupiravir, which is 800 mg every 12 hours.18 This would correspond to a dose per kilogram of 10 to 13.3 mg/kg twice daily for adults weighing 60 to 80 kg. As no pharmacokinetic information is available in relation to cats, we have chosen the dosage for cats based on the assumption that metabolism of drugs in cats is equivalent to metabolism in humans.

Owners were instructed to administer the tablets twice a day with 12 hours between doses. The expected standard duration of treatment was 84 days according to study GS-441524.10

2.4 Measurements

Owners were instructed to record body weight, body temperature, physical activity, appetite, and voiding/urinating daily and were asked to visit the clinic at 1, 2, 6, and 10 weeks. The following laboratory tests were required at each visit: red and white blood cell count, hemoglobin, hematocrit (HCT), AGP, total protein, albumin, aspartate transaminase (AST), alanine transaminase (ALT), total bilirubin, creatinine, blood urea nitrogen (BUN ) and the A/G ratio. Samples were analyzed in the clinic using a Catalyst One chemistry analyzer and a ProCyte One hematology analyzer (both IDEXX Laboratories, Westbrook, Maine). The A/G ratio was determined either from a whole blood plasma sample or from a fractionated protein sample. We performed abdominal and thoracic ultrasound evaluation of each cat at baseline and after 2, 6, and 10 weeks of treatment using a Prosound α7 (Aloka, Japan), including assessment of cardiac function (fractional shortening, left atrial to aortic diameter ratio, and valvular regurgitation).

2.5 Adverse Events

Any abnormal laboratory test values or medical events that occurred during treatment were considered adverse events and decisions were made to continue/discontinue treatment.

2.6 Statistical analysis

As this is a case series, no statistical calculations were performed other than descriptive statistics.

2.7 Ethics

All owners provided written informed consent prior to initiation of treatment. The experimental use of molnupiravir was approved by our Institutional Animal Study Review Committee.

3 RESULTS

3.1 Characteristics of the disease and treatment

Eighteen cats completed treatment by August 4, 2022 and are included in this summary report.

The presentation of the 18 cats is summarized in Table 1 and Table S1. The median age was 6.5 (range: 3-93) months. All 18 cats had a low serum A/G ratio, 16 cats had a loss of appetite, and 14 cats had mild to severe anemia by hemoglobin level and HCT. Thirteen cats had effusive FIP and 5 cats had non-effusive FIP. Neurological or ocular signs suggestive of FIP were present in 3 cats before treatment, including epileptic seizures/neurological signs (No. 8), blunted postural reflexes (No. 10), and slow pupillary reflex (No. 18) (Table S1). All but 2 cats (#8 and #15) were treated exclusively on an outpatient basis. Cat no. 8 was hospitalized from day 37 for 3 days due to jaundice. Cat no. 15 required hospitalization for 5 days after starting treatment due to anemia and jaundice accompanied by increased bilirubin concentration and ALT activity. During hospitalization, the cat received molnupiravir as scheduled, was hydrated with Ringer's solution, and treated with oral ursodeoxycholic acid (Towa, Japan) 10–15 mg twice daily to reduce bilirubin. There was no evidence of intravascular hemolysis (HCT remained stable), and microscopic examination of blood smears was negative for hemotropic mycoplasma infection.

TABLE 1. Basic characteristics of the cats in the described case series.

Age at disease onset, months, median (range)6.5 (3-93)
Breed, n (%)
Housecat9 (50.0)
Exotic shorthair2 (11.1)
British Shorthair2 (11.1)
Other5 (27.8)
Sex, n (%)
Male not neutered/male neutered4 (22.2)/7 (38.9)
Female not spayed/female spayed2 (11.1)/2 (11.1)
Weight in kg, mean (SD)2.72 (0.77)
Duration from onset of illness to initiation of treatment, days, median (range)16.5 (2-49)
Effusive type, n (%)13 (72.2)
Pyogranulomatous lesions in the abdominal cavity, n (%)5 (27.8)
Neurological manifestations of FIP, n (%)2 (11.1)
Ocular symptoms of FIP, n (%)1 (5.6)
Temperature, °C, mean (SD)39.3 (0.9)
Hematocrit, %, mean (SD)27.3 (8.1)
Albumin/globulin ratio, mean (SD)0.35 (0.10)
Sample type, n (%)
Abdominal effusion11 (61.1)
Pleural effusion1 (5.6)
FNA of a pyogranulomatous lesion2 (11.1)
Full blood3 (16.7)
None1 (5.6)

The attending physician decided to extend the treatment to 99 days for cat no. 1. Consciousness disturbances appeared on day 8 in this cat and the dose was subsequently increased to 40 mg/kg. This symptom disappeared on the 15th day; however, the A/G ratio with the fractionated protein sample did not return to normal. On day 99, although the A/G ratio was still below the reference range (0.6), the clinician decided to stop treatment because the cat showed no clinical progression or deterioration.

3.2 Outputs

Clinical response in 14 cats was rapid. Dosing, findings during treatment, and outcomes in these animals are summarized in Tables S2 and S3. The fever subsided and the appetite returned within 2-3 days after the start of treatment. Remissions were also achieved in cats with severe clinical signs. Among them were cats no. 8, 17 and 18, which had pyogranulomatous lesions ≥ 2 cm in size, cat no. 4, which had severe anemia and a low A/G ratio, cat no. 14, which had a pleural effusion and difficulty breathing, and cat no. 15, who had an enlarged kidney. The pyogranulomatous lesions shrank or were undetectable on ultrasound in all 5 cases, and laboratory values returned to normal in all cats. Three cats had neurological signs of FIP before treatment. Cat no. 12 had no neurological symptoms of FIP before treatment, but had an epileptic seizure on day 7. The dosage was subsequently increased to 40 mg/kg. On the 2nd day, on the slit lamp at cat no. 7 found anisocoria that was probably related to uveitis. The dosage of molnupiravir was increased to 40 mg/kg from day 15, and all neurological or ocular signs of FIP resolved within 15 days.

Of the 14 cats that achieved remission, no relapses occurred through August 3, 2022, during 55 to 107 days of post-treatment follow-up. Three cats died (No. 2, No. 11 and No. 16) and one (No. 13) was euthanized; all these cats had the effusive form of FIP but had no neurological or ocular signs of the disease. All died within one week of starting treatment.

3.3 Security

Alanine transaminase activity higher than the reference value was found in 4 cats; the value of each of them was 286 U/l (cat #8 on day 37), 283 U/l (cat #9 on day 9), 154 U/l (cat #10 on day 7), and 117 U/l (cat No. 17 on the 9th day). Three cats with early ALT elevations on days 7 to 9 recovered without the need for intervention. In cat no. 8 developed jaundice on day 37 and was hospitalized for 3 days.

No abnormalities in BUN or creatinine concentrations were noted during treatment with molnupiravir.

4 DISCUSSION

In our series of cats with presumptive FIP treated off-label with a molnupivir compound, 14 of 18 cats achieved remission and remained in remission for up to 107 days of observation at the time of writing. Four cats showed signs of potential hepatic adverse effects; 3 cats developed ALT activity above the reference range during the first 7 to 9 days of treatment, all of which resolved without treatment, and 1 cat developed jaundice requiring hospitalization on day 37 of treatment.

The approved human formulation of molnupiravir is in 200 mg capsule form, but for animals it must be divided into smaller doses to facilitate administration of an appropriate dose based on body weight. We decided to prepare molnupiravir in the form of small tablets to simplify administration. We hypothesized that cats might refuse to swallow the drug in powder form or in aqueous solution, and it might be difficult for owners to administer the entire powder dose each time.

The minimum effective dose of molnupiravir in FIP is recommended to be 4.5 mg/kg PO every 12 hours for cats without neurological/ocular signs of disease, increasing to 12 mg/kg PO every 12 hours for cats developing ocular or neurological signs. symptoms of FIP.17 Others recommend a dose of 25 mg/kg every 24 hours for dry/wet FIP, 37.5 mg/kg every 24 hours for ocular FIP, and 50 mg/kg every 24 hours for neurological FIP.16 Since none of these recommended dosages have been established in prospective controlled studies, the dosage in this case series was determined by the author based on these estimates, adult dosages, and his experience. Nevertheless, the dosage used in our case series (10 mg/kg twice daily for cats with effusive FIP, 15 mg/kg twice daily for cats with non-effusive FIP or pyogranulomatous lesions, and 20 mg/kg twice daily for cats with neurological or ocular signs FIP) appears to be effective and safe and may help guide dosing in future clinical trials.

Four cats died during this study. Each of these cats had the effusive type of FIP; however, considering that some cats that survived had symptoms as severe or even more severe than those that died, no signs were found to predict early death. Unfortunately, the attending veterinarian was given little information about the deaths of the 3 cats that died at home, and no post-mortem examinations were performed. One cat (#2) died after vomiting the drug on day 6, so it is possible that this animal had swallowing problems.

The use of GS-441524 in 31 cats with FIP, of which 26 cats completed at least 12 weeks of treatment, resulted in remission in 25. 10 Eight of the 26 cats relapsed or became reinfected within 3 to 84 days after this period. . The length of observation in our case series is shorter than in study GS-44152410; however, observation of cats in our series is currently ongoing and more cats with FIP are being treated with molnupiravir. Further observation will provide data on longer-term efficacy. The major adverse events reported with injection in study GS-441524 were injection site reactions in 16 of 26 cats.10 Because the treatment in our study was administered orally, no injection site reactions occurred in any of the cats in our series. In our series, the most frequent adverse event during treatment was an increase in ALT activity. However, longer-term follow-up is necessary to more adequately assess liver-related reactions, and a larger group of animals is needed to more fully assess the adverse effects of molnupiravir.

Molnupiravir is active against SARS-CoV-2 and other RNA viruses19 and in cell culture it creates only low resistance.20-22 The efficacy of oral molnupiravir was evaluated in a phase 3 randomized control trial in 1,433 people with COVID-19, with a lower percentage of hospitalizations or deaths by day 29 in the molnupiravir group compared to placebo.18 Another important clinical question is whether molnupiravir-resistant viruses can develop and how many cats relapse or reinfection after treatment.

All owners who provided informed consent to participate were included in this study, so the risk of any bias should be minimal. Nevertheless, selection bias should be considered as this case series was enrolled in a single center in Chiba Prefecture, Japan. Another potential limitation of our case series is that the diagnosis of FIP was probable in all cases. Cats can have FCoV viremia without FIP, so RT-PCR detection of FCoV RNA is not specific for FIP.7 although this technique has a high sensitivity (90 %) and specificity (96 %) for FIP when applied to FNA specimens.23 In our series, the combination of RT-PCR with clinical signs and other serum biochemical tests, including a low A/G ratio, was highly suggestive of FIP.7 This case series suggests that molnupiravir may be an effective and well-tolerated treatment for FIP.

Additional information

The fileDescription
jvim16832-sup-0001-Tables.pdf
PDF document, 317.1 KB		Table S1. Feline demographics and disease status before treatment.
Table S2. Overview of the course of treatment.
Table S3. Test values obtained at the first visit and the last test, based on which the decision was made to stop treatment.

References

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