Cat Not Improving on FIP Treatment? Week 2 Expectations

Key takeaway: A cat that still looks unwell after two weeks on GS-441524 is common and usually not a sign of failure. Fever and appetite often improve within the first few days, but weight gain, energy, and blood values can take three to six weeks to normalise, and neurological or ocular cases are typically slower. Stay on the daily dose, keep your veterinarian informed, and judge progress by trend, not by a single day.

A cat resting comfortably at home.

Why does my cat still look unwell after two weeks on GS-441524?

Slow visible improvement in the first two weeks of Feline Infectious Peritonitis (FIP) treatment is normal for many cats and does not mean GS-441524 is not working. The drug works by suppressing viral replication, and while some internal markers respond quickly, the outward signs your eyes track (coat quality, muscle mass, playfulness) rebuild more gradually.

Most caregivers expect a dramatic turnaround. In reality, early recovery is often a mix of clear wins and stubborn symptoms sitting side by side.

GS-441524 is the antiviral at the core of modern FIP treatment, with a 92% success rate reported by UC Davis (Pedersen, 2019) for injectable monotherapy. That success rate is measured across the full 84-day protocol, not across the first fortnight.

What should improve in the first two weeks, and what takes longer?

In the first two weeks, fever, appetite, and alertness usually improve first, while weight, muscle, energy, and abnormal blood values take longer to catch up. This staggered timeline is one of the most misunderstood parts of early FIP treatment.

Use the pattern below as a general guide, then confirm your own cat's picture with your veterinarian.

Sign	Typical early response	What to watch for
Fever	Often within 24 to 72 hours	A fever that never breaks or returns
Appetite	Usually improves in the first week	Complete refusal to eat past several days
Energy and alertness	Gradual over the first two to three weeks	No change at all after two weeks
Weight and muscle	Rebuilds over weeks, not days	Continued steep weight loss
Fluid (wet FIP)	Effusion often reduces over one to three weeks	Rapidly worsening breathing

A cat can eat well and still look thin and tired at day 14. That combination is common and does not, on its own, mean GS-441524 is not working early in treatment.

If you want a day-by-day sense of the earliest phase, our guide on what to expect during your cat's first week on GS-441524 treatment sets a realistic baseline before you judge week two.

Does the type of FIP change how fast my cat recovers?

Yes. The form of FIP your cat has strongly influences how quickly you see improvement, because each form affects different tissues and carries a different dose in the standard protocol. FIP takes four forms, and each shapes both the treatment plan and the pace of recovery.

The CureFIP GS-441524 Antiviral Injectable is dosed by type, and the four rows below mirror the four forms directly.

Wet / Effusive FIP

Wet FIP involves fluid buildup in the abdomen or chest, and it often shows some of the fastest early responses because reducing effusion is measurable. The injectable dose for wet FIP is 6 mg/kg once daily by subcutaneous injection.

Even so, fluid can take one to three weeks to visibly recede, and a cat can still look bloated or breathe a little heavily in the first days.

Dry / Non-effusive FIP

Dry FIP has no obvious fluid, which makes early progress harder to see with the naked eye. The injectable dose for dry FIP is 8 mg/kg once daily.

Because dry FIP progress is often internal (organ inflammation settling, blood values shifting), your veterinarian's bloodwork matters more than your day-to-day observation in the first two weeks.

Ocular FIP

Ocular FIP affects the eyes, causing colour change, cloudiness, or vision problems, and it typically responds more slowly than wet FIP. The injectable dose for ocular FIP is 10 mg/kg once daily.

The higher dose reflects the need to reach protected sites, so patience in the early weeks is especially important here.

Neurological FIP

Neurological FIP affects the brain and spinal cord, producing wobbliness, seizures, or behaviour change, and it is usually the slowest form to show visible improvement. The injectable dose for neurological FIP is 10 mg/kg once daily.

Because the drug must cross into the central nervous system, do not be alarmed if neurological signs lag behind other improvements in the first two weeks. If you are unsure which form your cat has, our complete guide to cat FIP symptoms can help you frame the conversation with your veterinarian.

How do I tell a slow response apart from treatment not working?

The key difference is direction: a slow response still trends upward over one to two weeks, while true non-response shows no improvement or active worsening across the same window. One flat day is not failure; two weeks of decline is a reason to reassess with your veterinarian.

Signs your cat is trending the right way, even if slowly:

• Fever has broken or dropped, even if energy is still low

• Appetite is returning, even in small amounts

• Weight has stabilised or started to climb

• Effusion (in wet FIP) is gradually reducing

• Bloodwork is moving toward normal at your veterinary recheck

Signs worth an urgent veterinary conversation:

• Persistent high fever past the first week of dosing

• Continued rapid weight loss

• Worsening breathing or new neurological signs

• Complete refusal to eat for multiple days

Getting the diagnosis right underpins all of this. Some cats plateau because the underlying condition was never FIP, so it is worth understanding common FIP misdiagnoses if progress stalls completely.

Why is my cat still not eating well two weeks in?

A reduced appetite at two weeks can reflect lingering nausea, inflammation that is still settling, or simply a cat that feels unwell overall, and it does not automatically mean the antiviral has failed. Appetite is usually one of the earlier signs to improve, but it can be inconsistent through the first fortnight.

Gentle, consistent feeding support matters here. Warming food, offering small frequent meals, and using strong-smelling options can help, and our appetite support guide for cats with FIP covers practical tactics for encouraging a reluctant FIP cat to eat.

Tell your veterinarian if your cat is eating far below normal for several days, since anti-nausea or supportive care may help while the antiviral does its work.

Should I change the dose or protocol if progress is slow?

No, you should not change the dose or stop the protocol on your own because progress feels slow; all dosing decisions belong with your veterinarian. The standard course runs 84 days (12 weeks) of daily treatment, and stopping early or altering the dose without guidance is a leading cause of relapse.

The GS-441524 Antiviral Injectable is available in two strengths, and both follow the same daily-injection, 84-day structure.

Product	Strength	Price	Schedule	Duration
GS-441524 Antiviral Injectable, 20mg/ml, 8ml	20 mg/ml	AU$79.00	1 subcutaneous injection per day, 7 days/week	84 days
GS-441524 Antiviral Injectables, 30mg/ml, 8ml	30 mg/ml	AU$99.00	1 subcutaneous injection per day, 7 days/week	84 days

If your cat is gaining weight during treatment, the dose may need recalculating, but only your veterinarian should adjust it. Weight gain is actually a good sign, and it is the reason dosing is reviewed across the protocol.

Some caregivers in Australia and New Zealand are also discussing oral options with their veterinarians, including dual antiviral therapy for FIP. The CureFIP Oral Capsules - Dual-Action Formula combine GS-441524 and EIDD-1931 and are dosed by weight band, with a 78.3% remission figure reported by Li and Cheah (2025) for the dual antiviral approach. That oral dual route is positioned for wet and dry FIP, and some regions note it is not recommended once ocular or neurological signs are present or when a cat cannot eat or defecate.

What can I do at home to support recovery in the early weeks?

The most useful things you can do at home are keep the daily dose consistent, track symptoms objectively, reduce stress, and attend every veterinary recheck. Small, steady inputs matter more than any single intervention in the first two weeks.

1. Give the injection at the same time each day, seven days a week, without gaps.

2. Keep a simple daily log of temperature, appetite, weight, and energy so you can see the trend.

3. Weigh your cat regularly, since dosing is based on weight and gains are meaningful progress.

4. Keep the environment calm, warm, and low-stress to reduce strain during recovery.

5. Attend all scheduled veterinary rechecks and share your log at each visit.

CureFIP has supported a network of 100,000+ cats treated since 2019, and the pattern is consistent: caregivers who track trends and hold the protocol steady weather the anxious early weeks far better. For a broader plan, our practical FIP survival strategies for Australian and New Zealand cat owners pulls the day-to-day routine together.

We are clear about what the data shows and what it does not: GS-441524 is the proven antiviral at the core of FIP treatment, but recovery timelines vary from cat to cat, and slow does not mean stalled.

FAQ

Is it normal for my cat to still look sick after 2 weeks on GS-441524?

Yes, it is common for a cat to still look thin or tired at two weeks even when GS-441524 is working, especially in dry, ocular, or neurological FIP. What matters is the overall trend across the two weeks, so judge progress by fever, appetite, and weight moving in the right direction rather than by a single day.

How long does GS-441524 take to work in FIP?

Fever and appetite often improve within the first few days of GS-441524 treatment, while weight, energy, and blood values typically take three to six weeks to normalise. The full course runs 84 days, and stopping early is a leading cause of relapse.

When should I worry that FIP treatment is not working?

Be concerned if your cat shows no improvement at all after two weeks, has a persistent high fever past the first week, keeps losing weight rapidly, or develops worsening breathing or new neurological signs. Contact your veterinarian promptly, since these patterns differ from a normal slow response.

Can I increase the dose to speed up my cat's recovery?

No, you should never change the GS-441524 dose on your own. All dosing decisions belong with your veterinarian, who will recalculate the dose if your cat gains weight or if the form of FIP requires it.

Why is neurological FIP slower to improve than wet FIP?

Neurological FIP is slower because the antiviral must reach the brain and spinal cord, which are protected sites, and this is why the injectable dose for neurological FIP is 10 mg/kg once daily. Visible improvement in coordination or behaviour can lag behind gains seen in wet FIP.

If your cat's early weeks feel slower than you hoped, you are not alone, and steady daily treatment paired with veterinary guidance is the most reliable path forward. To explore treatment options and talk through your cat's progress with people who understand FIP, reach out to the CureFIP Oceania team and keep your own veterinarian closely involved in every decision.