New treatment turns the tables on Feline Infectious Peritonitis

Clinicians at the Hospital for Small Animals have successfully treated over 50 cats with Feline Infectious Peritonitis (FIP) since 2021 and have advised first-opinion vets dealing with hundreds more cases, thanks to the availability of anti-viral drugs used to treat covid-19 in humans.  

The Specialist-led Internal Medicine team report a success rate of over 85 per cent following treatment with a 12-week protocol of GS-441524, the main plasma metabolite of Remdesivir, and occasionally with other antivirals. 

This has drastically improved the prognosis of FIP as a condition previously considered fatal in almost all cases. 

The clinicians are now looking to develop a patient-centred treatment programme that may lower the current treatment duration in the future. 

The anti-viral drugs Remdesivir, then its active ingredient GS-441524, have been available under the UK veterinary cascade since 2021. 

One of the first cats that benefited from treatment with GS-441524 was Rebus, who was referred to the Hospital in May 2022. The 10-year-old domestic short hair cat was suffering from rapid weight and muscle loss, inappetence and lethargy. He was also drinking and urinating excessively.  

Initial tests showed that Rebus was hypoalbuminaemic (18.8g/L) and markedly hyperglobulinaemic (116.6g/L) which was highly suggestive of FIP. His total protein level was also double the reference interval and pyogranulomatous inflammation was detected in his kidneys, spleen, liver and lymph nodes which was consistent with FIP.  

Immunohistochemistry for feline coronavirus (FCoV) was positive, which confirmed the diagnosis.  

Supportive treatment including intravenous (IV) fluids, pain medication and medical appetite stimulation was started immediately. Rebus then received Remdesivir by subcutaneous injection, before moving onto oral treatment with the antiviral GS-441524 once it was approved for use. 

At the end of the standard 12-week oral treatment period, Rebus’s globulin levels were still high, so his treatment was extended for a further eight weeks. 

Rebus’ condition was continually monitored by the Internal Medicine Service throughout his treatment, including assessment of the main inflammatory marker - alpha-1-acid glycoprotein (AGP) - which decreased with successful treatment. Rebus had evidence of kidney damage before treatment began, so his creatinine values were also closely monitored whilst he was taking the anti-viral medication.  

Within three months, Rebus had made a full recovery from FIP, and three years on he continues to live a full and active life, whilst receiving ongoing care for his chronic kidney disease. 

Feline Coronavirus (FCoV) remains ubiquitous in the cat population. It is estimated that 40-50 per cent of cats are carriers of the virus and up to 80-100 per cent in a multi-cat household.  

While predicting when enteric FCoV infection develops into the clinical picture of FIP in individual cases remains challenging, treating FIP used to be nearly impossible, with the infection leading to fatal outcomes in the vast majority of cats before the availability of GS-441524.  

The Hospital is one of the leading centres for FIP expertise in the UK and is undertaking key research to further improve treatment options.