FIP Treatment Protocols
Although GS-441524 is currently the most commonly used antiviral treatment for FIP, several other antiviral options are also available. Choosing the appropriate antiviral and treatment modality may depend on the patient's form of FIP and degree of stability, the owner's ability to administer the various forms, availability and veterinary regulations in your country or state.
GS-441524
This is the most commonly used treatment for FIP, as well as the most documented. It is effective for all forms of FIP (with correct dosing)
GS-441524 is available as either SC injections or pills.
The typical protocol is 12 weeks (84 days) of continuous treatment with the following SC dosages:
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5-6 mg/kg for cases without ocular or neurological involvement
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8 mg/kg (minimum) for ocular FIP cases
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10 mg/kg (minimum) for neurological FIP.
Ocular and neurological cases in particular may require higher doses as there is variation between cats in the amount of GS-441524 that crosses the blood/brain barrier -- ranging from about 7% to 21%.
Oral GS-441524 dosages are roughly double the SC equivalent -- however some suppliers label doses by effective dose. Click here for more info.
Remdesivir
Remdesivir has only recently seen usage for FIP, and is often used only for the start of treatment and then combined with GS-441524. This treatment is primarily in use in Australia and the UK where Remdesivir is legal and available to veterinarians for prescription.
The treatment protocol is 12 weeks of treatment, however frequently Remdesivir is used only for the initial few weeks, and cats switch to GS-441524 oral tablets for the remainder of treatment.
Dosing is as follows:
10-12 mg/kg IV or SC for non-ocular/neurologcal FIP
15 mg/kg IV or SC for ocular FIP
20 mg/kg IV or SC for neurological FIP
Note that IV administration does have approximately 10% greater chance of worsening existing pleural effusion, or causing new occurrence of pleural effusion so close monitoring is warranted.
For more information on treating with Remdesivir we recommend this excellent pdf put together by vets and researchers in the UK and Australia.
GC376
GC376 is a 3CLPro inhibitor and was the first antiviral documented to successfully cure FIP. It is typically less commonly used as a first line of treatment as it has comparatively low penetration of the blood/brain barrier, making it less effective for neurological FIP cases. It has however found use paired with GS-441524 as part of combination therapy to combat viral resistance to GS-441524.
Due to poor oral absorption, GC376 is only administered as a sub-cutaneous injection.
For non-neurological FIP, GC376 is dosed at 15-20 mg/kg SC BID.
For cats with viral resistance to GS-441524, GC376 is added to the current GS-441524 dosage at a dosage of 20 mg/kg SC BID regardless of form of FIP. This is sufficient for most cats, including many neuro FIP cats, but some will need higher dosages. If this fails to achieve remission of clinical signs or bloodwork is concerning, the GC376 dosage is increased by 10 mg/kg increments to as high as 50 mg/kg SC BID.
Molnupiravir
This is a new and experimental option that has become available most recently --while it seems effective in limited testing, overall effectiveness has not been established, and there are concerns that it could be mutagenic. A study has been published showing it to be an effective rescue treatment for cats that have failed treatment with other antivirals for FIP. Currently it is mostly used as an alternative for cats who have developed resistance to other antiviral treatment.
While the dosing range has not yet been definitively established, the minimum effective dose appears to be:
6-8 mg/kg PO BID for non-ocular/neurological FIP
8-12 mg/kg PO BID for ocular FIP
10-15 mg/kg PO BID for neurological FIP
Due to concerns about long term usage and mutagenic properties, including accelerating emergence of viral variants of concern, it is recommended that the lowest effective dosage be used. Unlike GS-441524, Remdesivir and GC376, it is teratogenic and should not be used in pregnant or breeding queens.
