Stabilization & Symptomatic Support
Providing good supportive care especially at the beginning of treatment can greatly improve the prognosis and allow even cats in critical condition to successfully complete treatment.
Short-acting steroids such as prednisolone or dexamethasone SP can be helpful in stabilizing a patient prior to or at the beginning of treatment for FIP. It is strongly recommended however they should be discontinued once the patient has begun to show improvement -- typically within the first week. Longer-term steroid use is strongly discouraged (unless concretely required) since:
it can mask the extent of symptom resolution, especially in cats with neurological FIP
once symptoms begin to resolve it is no longer beneficial
steroid use may interfere with the development of a protective immune response to the FIP virus
Use of long-acting steroids such as Depo-Medrol is strongly discouraged.
Note that there are indeed cases where steroid use is appropriate later into treatment, for example reducing ICP in cats with severe neurological FIP.
When pleural effusion is present, therapeutic thoracocentesis is necessary and recommended to relieve symptoms if the patient is presenting with dyspnea. No further intervention may be needed as thoracic fluid tends to return more slowly than with abdominal effusions and typically symptoms related to thoracic effusions resolve after 7-10 days. However this is variable and it is recommended that the owner be counseled on monitoring and being prepared to repeat the procedure if necessary.
Therapeutic abnominocentesis is generally not recommended unless the fluid is compressing the chest and interfering with breathing, in which case it is recommended to remove only as much as is needed to relieve symptoms. Typically abdominal effusion tends to return fairly rapidly, limiting the therapeutic usefulness of abnominocentesis. Repeated drainage of abdominal effusions may deplete proteins and cause harmful shifts in fluid and electrolyte balances in severely ill cats.
Pericardial effusion is a more rare presentation, but when present may require pericardiocentesis.
Anemia accompanying FIP is usually fairly mild, and does not require much intervention. However in some cases a more severe anemia may require transfusion. It is also important to remember that cats with FIP are immunocompromised and may have secondary conditions that could cause anemia, such as mycoplasma.
The anemia can be caused by several mechanisms, including secondary autoimmune hemolytic anemia (AIHA), and chronic inflammation. Generally all but the most severe anemia resolves well without additional treatment or supplementation. In cats with severe intestinal changes, Heinz bodies can be found in large numbers in erythrocytes due to decreased absorption of vitamin B12 leading to hemolysis. In this case B12 supplementation may be useful, but in most cases is un-necessary.
Seizures and other Neurological Symptoms
For neurological FIP cats presenting with seizures it is important to initiate supportive anti-seizure treatment to be used concurrently with beginning FIP antiviral treatment. Once the underlying inflammation due to FIP is under control, the patient can be weaned off of these medications. Often this can be started around 6-8 weeks into treatment assuming response to treatment has been good. In most cases seizures can be completely resolved with treatment, but a few cats may have residual damage and may require life-long anti-seizure therapy.
Steroids can also play an important part in stabilizing neurological FIP patients. While they may be required slightly longer than for other case, the same guidelines apply -- once the cat is stable and neurological symptoms are clearly improving, steroids should be discontinued.
Cats presenting with ocular symptoms may requires supportive treatment with topical medications (for example pred acetate) to counteract severe inflammation and increased intraocular pressure (glaucoma) in some cases.
In cases where severe glaucoma has occurred and enucleation is necessary, it is recommended to postpone surgery until the patient is stable and doing well on antiviral therapy. Weeks 8-10 of treatment is often a common time to schedule such surgeries.
Inappetence and Nutritional Support
Cats diagnosed with FIP often present with low or no food intake. Often they may have been in this condition for more than a few days, thus exacerbating the problem. Most FIP experiencing inappetence will benefit from a short course of anti-nausea medication and an appetite stimulant. Typically these are only required for a couple of days, but in some cases may be needed for up to a week.
In severely ill cats, placement of a nasogastric tube or esophageal tube may be beneficial as a temporary means to ensure that the cat is getting adequate nutrition. This can be particularly true for severely neurological cats who may not be able to eat and may have decreased ability to swallow, as syringe feeding by the owner carries a higher risk of aspiration.
Diarrhea is a common symptom which presents with FIP. While it may resolve on its own, a good probiotic or diet change may be helpful with resolution.
Note also that it is common for FIP cats to present with secondary infections and infestations, (due to immune compromise) some of which may be the actual cause of diarrhea. Running a fecal panel may be warranted to detect these issues so that they can be treated. It is safe to de-worm a cat during treatment. Treatment of fecal parasites (giardia, coccidia) is also safe, however exercise care when using metronidazole as it can have neurological side effects which could be confused with FIP symptoms, clouding the diagnostic picture.
There is no evidence that any dietary or other supplementation is necessary or beneficial for successfully treating FIP, nor that any additional supplement in addition to the antiviral drugs improves treatment outcomes.