FIP Symptoms Checklist: Early Signs to Advanced Stages
Feline Infectious Peritonitis ("FIP") symptoms usually begin with vague signs like a fever that will not break, fading appetite, weight loss, and low energy, then progress into one of four recognized forms: wet, dry, ocular, or neurological. The earlier you recognize these signs and reach your veterinarian, the sooner a GS-441524 based treatment plan can begin. This checklist walks you through FIP symptoms stage by stage, so you know what to watch for and when to act.
A cat resting comfortably at home.
What are the first warning signs of Feline Infectious Peritonitis (FIP)?
The earliest signs of Feline Infectious Peritonitis (FIP) are usually non-specific: a persistent fever that does not respond to antibiotics, a drop in appetite, gradual weight loss, and unusual tiredness. These signs are easy to miss because they look like many ordinary illnesses, which is exactly why they matter.
FIP is caused by a mutated form of the common feline coronavirus (FCoV). Most cats carry the harmless intestinal coronavirus at some point, but in a small number of cats it mutates and triggers FIP.
Early FIP symptoms in cats tend to include:
A fluctuating fever that keeps returning and does not respond to antibiotics
Reduced or picky appetite over several days
Steady, unexplained weight loss
Lethargy and less interest in play or interaction
A dull, poor coat and a generally "off" look
Slowed growth in kittens and young cats
If your cat shows a cluster of these early FIP symptoms, especially a young cat under two years old, it is worth a prompt veterinary visit. You can read a plain-language overview in our guide to what FIP in cats actually is.
What are the four forms of Feline Infectious Peritonitis (FIP)?
Feline Infectious Peritonitis (FIP) takes four distinct forms: wet (effusive), dry (non-effusive), ocular, and neurological. Each form has its own hallmark symptoms, and the form your cat has shapes the treatment plan and the dose your veterinarian chooses.
The four forms can overlap, and a cat may shift from one to another as the disease advances. Below is what each form looks like.
Wet (effusive) FIP
Wet (effusive) FIP is the form defined by fluid buildup inside the body, most often in the abdomen or the chest. It tends to progress quickly and is frequently the first form caregivers notice.
Watch for:
A swollen, rounded, or distended belly that feels full
Labored or rapid breathing when fluid collects in the chest
Fever, weight loss, and low energy alongside the swelling
A "pot-bellied" look even as the cat loses weight elsewhere
Dry (non-effusive) FIP
Dry (non-effusive) FIP produces little or no fluid and instead causes inflammatory lesions on internal organs. It often develops more slowly, which can make it harder to pin down.
Watch for:
Ongoing fever that comes and goes
Persistent weight loss and poor appetite
Signs tied to the affected organ, such as jaundice with liver involvement or digestive upset
General decline without the obvious belly swelling of the wet form
Ocular FIP
Ocular FIP is a distinct form that targets the eyes and may appear on its own or alongside other forms. The eye changes are often the first clear clue something serious is happening.
Watch for:
A change in iris color (for example a brown or muddy tint appearing)
Cloudiness inside the eye
Inflammation inside the eye (uveitis)
Vision loss from lesions within the eye
A color change in the eye is an ocular sign, not a neurological one, so flag any shift in your cat's eyes to your veterinarian right away.
Neurological FIP
Neurological FIP is a separate form that affects the brain and spinal cord. It is one of the more advanced and serious presentations and calls for careful veterinary management.
Watch for:
Seizures
Head tilt
Loss of balance and coordination
Partial or full paralysis
Disorientation or sudden behavior changes
How do FIP symptoms progress from early to advanced stages?
FIP symptoms generally move from vague and systemic in the early stage to form-specific and severe in the advanced stage. The early phase looks like a general illness, the middle phase reveals which form is taking hold, and the advanced phase brings the defining signs of the wet, dry, ocular, or neurological form.
Here is a simple way to think about the progression:
Early stage: A fever that will not clear, fading appetite, gradual weight loss, and low energy. Nothing points clearly to FIP yet.
Developing stage: The picture sharpens. Fluid may begin to collect (wet form), eye changes may appear (ocular form), or organ-related signs emerge (dry form).
Advanced stage: Form-defining signs become pronounced. Belly or chest fluid causes visible swelling or breathing trouble, eyes show marked inflammation or vision loss, or neurological signs such as seizures and loss of balance set in.
Because FIP can advance quickly, especially the wet form in young cats, time matters. The sooner a diagnosis is confirmed and treatment begins, the better positioned your cat is.
When should you take a cat with suspected FIP symptoms to the vet?
Take your cat to the veterinarian as soon as you notice a combination of persistent fever, weight loss, appetite loss, and any form-specific sign such as a swollen belly, eye color change, or balance problems. FIP is not something to watch and wait on, because the disease can escalate within days.
Your veterinarian may use bloodwork, fluid analysis, imaging, and other tests to build the diagnosis. There is no single quick test that confirms FIP on its own, so the full clinical picture matters.
Evidence shows that outcomes with GS-441524 are strongest when treatment is matched to the FIP form and started without delay. Across the whole treatment network, more than 100,000 cats have been treated since 2019, including cats treated with GS-441524.
What treatment follows an FIP diagnosis?
Once Feline Infectious Peritonitis (FIP) is diagnosed, the proven path is antiviral treatment built around GS-441524, given under veterinary supervision. GS-441524 is the antiviral at the core of modern FIP treatment, and the dose is chosen for the specific form your cat has.
The standard injectable protocol is 1 subcutaneous injection per day, 7 days a week, for 12 weeks (84 days). The daily dose is set by the FIP form.
FIP form | GS-441524 daily dose | Route and schedule |
Wet (effusive) FIP | 6 mg/kg | 1 subcutaneous injection daily, 84 days |
Dry (non-effusive) FIP | 8 mg/kg | 1 subcutaneous injection daily, 84 days |
Ocular FIP | 10 mg/kg | 1 subcutaneous injection daily, 84 days |
Neurological FIP | 10 mg/kg | 1 subcutaneous injection daily, 84 days |
This 6/8/10 mg/kg standard is consistent with current clinical practice. Gokalsing et al. 2025 found the best outcomes within the 5 to 10 mg/kg once-daily range, adjusted for FIP type and for neurological or ocular signs.
Injectable GS-441524 options and prices
The GS-441524 subcutaneous injectables come in several concentrations so your veterinarian can match volume to your cat's weight and form:
GS-441524 Antiviral Injectables | 15mg/ml, 8ml, $49.00
GS-441524 Antiviral Injectables | 20mg/ml (8ml, 10ml), $69.00
GS-441524 Antiviral Injectables | 30mg/ml (8ml, 10ml), $89.00
GS-441524 Antiviral Injectables, 40mg/ml (8ml, 10ml), $119.00
There is also a version with added vitamin B12 at the same dosing and indications: GS-441524 Antiviral with Vitamin B12 | 20mg/ml at $75.00 and GS-441524 Antiviral with Vitamin B12 | 30mg/ml at $95.00. The B12 is an addition for support, not a separate antiviral.
The evidence behind injectable GS-441524 is strong. In Pedersen et al. 2019 (J Feline Med Surg 21(4):271-281), 24 of the 26 cats that completed injectable GS-441524 treatment remained healthy, a 92% rate, meaning more than 9 out of 10 cats that completed injectable GS-441524 treatment stayed healthy. You can see a detailed breakdown in our article on the GS-441524 success rate and what the UC Davis trial shows.
In the larger Ansari Mood et al. 2025 cohort of 629 cats on GS-441524 for at least 12 weeks, survival reached 94.12%, so more than 9 out of 10 cats survived in that study.
The oral capsule option after the injection phase
For many cats, an oral option follows the first stretch of injections. The Cure FIP™ Oral Capsules combine GS-441524 + EIDD-1931, and the key advantage is simple dosing: one capsule a day chosen by your cat's weight class, with no mg math and no counting capsules. One pill for one weight class.
Weight class | Dosing |
0 to 2.5 kg (0 to 5.5 lb) | 1 capsule per day |
2.5 to 5 kg (5.5 to 11 lb) | 1 capsule per day |
over 5 kg (over 11 lb) | 1 capsule per day |
The Cure FIP™ Oral Capsules are priced at $129.00, with a recommended 12-week course. They are commonly used after 2 to 4 weeks of GS-441524 injections, including in ocular and neurological cases, or once the cat is stable.
Because the dual capsule contains EIDD-1931, it is not for cats that are vomiting or have diarrhea, cats under 1 year old with wet (effusive) FIP, cats that cannot eat or defecate normally, or pregnant, nursing, or breeding cats. Our own data from 46 treated cats showed a 78.3% remission rate on the dual antiviral, meaning about 8 out of 10 cats on the dual antiviral reached remission.
To compare routes and build a plan with your veterinarian, see our overview of the best treatment for FIP in cats. Every course follows the protocol for your cat's product, under veterinary supervision, and we are clear about what the data shows and what it does not: success rates are statistics, not promises.
Things to avoid during FIP treatment
During FIP treatment, your veterinarian will typically advise against certain products that can interfere with care:
Fluoroquinolone antibiotics
Spot-on flea medications
Lysine and immune boosters
FAQ
What are the earliest FIP symptoms in cats?
The earliest FIP symptoms are a persistent fever that does not respond to antibiotics, fading appetite, gradual weight loss, and low energy. These vague signs often appear before the form-specific signs of wet, dry, ocular, or neurological FIP, so a cluster of them in a young cat warrants a prompt veterinary visit.
Can a cat have more than one form of FIP at once?
Yes. Feline Infectious Peritonitis (FIP) takes four forms, wet, dry, ocular, and neurological, and they can overlap or shift over time. For example, a cat may show abdominal fluid along with eye changes, which is why your veterinarian evaluates the whole clinical picture before setting the dose.
Is a swollen belly always a sign of FIP?
A swollen belly is a classic sign of wet (effusive) FIP, where fluid collects in the abdomen, but it can also stem from other conditions. Your veterinarian can analyze the fluid and run additional tests to determine whether FIP is the cause.
How long does FIP treatment take?
The standard GS-441524 injectable protocol runs 12 weeks (84 days), with 1 subcutaneous injection per day, every day. An oral capsule course is also recommended for 12 weeks, often started after 2 to 4 weeks of injections, all under veterinary supervision.
Is there any guarantee my cat will be cured?
There are no guarantees in medicine, and the figures we share are statistical success rates rather than promises. The only guarantee we offer is that you can cancel any time before your order ships for a full refund, and all treatment decisions should be made with your veterinarian.
If your cat is showing any of these warning signs, you do not have to face it alone. Learn more about the GS-441524 based treatment options and talk with us or your own veterinarian by visiting the CureFIP USA treatment resources, where clarity and your cat's recovery come first. Acting early gives your cat the best chance to eat, play, and come back to being themselves.
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