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Visit to the Vet

Monitoring Treatment

Best Practices for Monitoring


A CBC and chemistry panel (at minimum including glucose, creatinine, BUN, albumin, globulin, ALT, ALP and total bilirubin) is recommended every 4- 6 weeks to monitor the progress of recovery during treatment.  Other panels may be added if there is suspicion of a secondary illness.  A FCOV titer is NOT necessary or recommended.


If clients have financial constraints and there is a positive clinical response to treatment then the clients may elect to forego some or all of the monitoring bloodwork as it is unlikely to change the outcome.

Weight checks and dosage adjustments

It is recommended that the cat be weighed at least weekly and dosage adjusted for weight gain.  This is particularly important as some cats may double or triple in weight because of significant weight loss prior to treatment or growth spurts.

Treatment Administration

Failure to reliably and regularly administer treatment, whether injections or pills is a common cause of treatment complication and failure.  It is important when talking with owners to emphasize the importance of adhering to a treatment schedule, and verifying that doses have successfully been administered to owners.

Dosage Adjustments

In general the dosage is unchanged throughout treatment, while the dose should be recalculated and adjusted as necessary on a weekly basis in response to weight changes.


However, in cases where a patient is not improving it may be necessary to raise the dosage of anti-viral. It is not appropriate to decrease the dosage of anti-viral as this increases the likelihood of resistance developing (an exception to this rule is when a cat is initially started on twice a day dosing or on a very high dose and then tapered to a lower frequency or dose within the first 3- 5 days).  


Dosages may need to be increased for the following reasons:

  • manifestation of neurological or ocular symptoms

  • lack of clinical improvement

  • lack of improvement in bloodwork

  • relapse of symptoms

In the case of effusions which are not resolving on the expected timeline, it is necessary to first eliminate other causes.

Before raising the dose it is recommended that you first confirm that the owner is administering the proper dose, and that the issue is not failure to inject or pill the cat.  Administration issues are common causes of treatment failure.


When increasing the dosage, it should be done in increments of:

  • 4-5 mg/kg (GS-441524 SC)

  • 4-5 mg/kg effective or 10 mg/kg actual (GS-441524 PO)

  • 10 mg/kg (GC376)

  • 4-5 mg/kg (Molnupiravir PO)

and if it elicits a positive response be continued for a minimum of 4 weeks.  This may mean increasing the length of treatment beyond 12 weeks.  

In the event of a relapse or major regression during treatment a minimum of 8 weeks from the point that dosage changes are made may be required.  This may require extending treatment beyond the usual 12 weeks.

Side effects

Note: less information about side effects is available for GC376, Molnupiravir and Remdesivir as they are currently used less often and have less formal study data available.

Cutaneous Sores, Lumps, Abscesses

This is the most commonly seen side effect with GS likely due to the low pH.  Sores are also seen to a lesser extent with GC376.

  • Sores

    • These can look quite ugly but generally heal well with little​ intervention.   In some cases, the sores have been quite large but it is extremely rare for cats to have require surgery for resolution. We recommend generally leaving sores alone other than other than removing hair from around the site, disinfecting it and preventing the cat from scratching it.  Some owners have had positive results with Duoxo calm or chlorhexidine mousse or Vetericyn spray.  Many cats on FIP treatment will wear shirts or recovery suits to prevent scratching or otherwise disturbing sores.

  • Lumps

      • Usually this is adipose tissue and does not require any intervention.  

  • Abscesses

    • These are often sterile but occasionally are infected and require a course of antibiotics​


Allergic reactions


Allergic reactions to FIP antiviral medications are very rare but occasionally reported.  In most cases the allergy appears to be to something in the drug preparation other than the antiviral itself, therefore switching to a different formulation or administration method (ie. injection to oral, or vice-versa) often resolves the issue.

The most common allergy manifestation is a rash, pruritus, acne, or other skin conditions.  In some reported cases it has been fairly severe.

A few cases of anaphylaxis have been reported associated with GS injections.

Elevated kidney values

Mild and transient BUN/creatinine elevation is reported relatively frequently with treatment using GS-441524.  In a few cats, primarily older cats or cats with pre-existing kidney disease more severe elevations can be seen.  Some cats will see elevated SDMA values, and sometimes impaired ability to concentrate urine which may or may not persist after treatment.  Monitoring of kidney values and urinalysis may be warranted in these cats. 


Subcutaneous fluid administration several times a week can help manage this during treatment, and often kidney values return to baseline once treatment has concluded.

Dental Development Delays

Treatment with GC376 has been noted to delay eruption of permanent teeth in cats treated before 16–18 weeks of age.

Treatment Completion

Determining if a patient is ready to complete treatment after 84 days or after extended treatment requires taking both clinical and diagnostic information into consideration.  It is extremely important that the entire picture of the cat's health be considered rather than assigning undue weight to any one slightly anomalous value on bloodwork. (For example, a slightly high globulin value or slightly  low A:G ratio.)  Treat the cat, not the bloodwork!


A CBC and chemistry panel is recommended to evaluate readiness for cessation of treatment. Ideally  the usual bloodwork markers for FIP should have returned to within normal limits.  More specifically:

  • Anemia should be resolved

  • Neutrophils should be within the normal range

  • % Lymphocytes at 20% or higher.  Lymphocytosis is often noted during and after treatment and is the effect of immune activation.  It may take months post-treatment for this to return to normal.  Lymphocytosis can be safely ignored within the context of FIP.

  • Hyperbilirubinemia resolved

  • Globulins within normal limits

  • An A/G ratio of 0.7 or higher is desirable, although some cats won't achieve this but may be cured.  An A/G level lower than 0.7 is less worrisome if it is the result of normal globulins and low (or low-normal) albumin rather than the reverse.


CBC and serum chemistry panels also include numerous other values and these can generally be safely ignored unless they are significantly elevated/decreased and associated with clinical signs.

Unless there is a specific concern, getting ultrasound or xrays at the conclusion of treatment is neither required nor recommended.  This is because terminal ultrasound findings small amounts of abdominal fluid, or vague irregularities in organs such as the kidneys,  spleen, pancreas, or intestines are more likely to be residual than signs of active disease.

Clinical Evaluation

The cat should be evaluated for outward manifestations of health.  For example:

  • Have neurological and ocular symptoms resolved?

    • Keep in mind, neurological and ocular FIP can leave behind some residual damage/symptoms​

  • Does the cat have a normal (or above normal) energy level?  

  • Does the cat have a normal appetite?

  • Has the cat gained weight?

If a cat does not substantially meet the above criteria, it is recommended to increase the dosage and extend treatment by a minimum of 4 weeks.  If resistance to the current antiviral is suspected, it may be desirable to switch the cat to a different antiviral treatment.  Antiviral resistance is typically indicated by either no response to the antiviral or a pattern of initial positive response followed by relapse which continues as the dose is raised progressively higher.  Aggressive dosage increases are sometimes able to overcome antiviral resistance, but large doses can complicate administration, making alternative antiviral therapies more attractive.


If there is concern that the cat is not ready to end treatment, but the concern is more minimal, a trial may be done at a higher dosage (or alternative antiviral) for 2 weeks at which point the cat is re-evaluated -- if the symptoms or labwork do not improve, you can more safely conclude they are not caused by active FIP disease and end treatment.  If improvement is seen, treatment should be extended for at least 2 more weeks.

Once a cat ends treatment, it is recommended that they be observed for 3 months to confirm whether the treatment has been successful.  During this time, a checkup and bloodwork are recommended every 4-6 weeks.

Relapse Treatment

The relapse rate seems quite low for cats who have successfully (and accurately) completed a full treatment (with high-quality preparations of the anti-viral.)  For cats treated with GS-441524, this seems to be less than 10% of cats that complete treatment.  For other protocols less data is available, but anecdotally seems similarly low.

The most likely time for a cat to relapse is within the first few weeks after treatment. There have been a very small number of reported cases where a treated cat has again been diagnosed with FIP after more than 3 months post treatment -- it is unclear whether these are a true relapse or a re-infection/re-mutation of FIP. 

Treating a Relapse

Relapses should be retreated for at least 8 weeks at a higher starting daily dosage than the previous round of treatment using the guidelines for dosage increases noted above for the particular antiviral.

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