FIP Treatment Week-by-Week: What to Expect from Day 1 to Day 14
- DVM Vien
- 4 days ago
- 3 min read
Quick answer: In the first 14 days of GS-441524 treatment, expect fever to break within 24–72 hours, appetite to return by day 3–7, energy to noticeably improve by day 7–10, and early weight gain by day 10–14. Wet FIP cats often show dramatic visible improvement in week 1 as fluid resolves; dry FIP cats improve more slowly through week 2. Bloodwork changes don't fully show up until day 28, so trust clinical signs in the first two weeks.
Day 1: First injection
The first injection is the most stressful one — for the owner and the cat. Most cats accept it with a brief startle. Use the 12-step technique from our injection guide. Don't expect visible improvement today. The cat may seem the same, slightly more tired (post-injection stress), or briefly off food.
Days 2–3: Fever breaks
The most reliable first sign that treatment is working: fever drops back to normal range (38–39°C). Take temperature once daily, ideally morning, to track. A fever that persists past day 3–4 needs review — contact us. Wet FIP cats may show subtly less abdominal distension; dry FIP cats may look the same but feel slightly more energetic.
Days 4–7: Appetite and energy return
Most cats start eating better by day 4–5 and showing increased interest in surroundings by day 6–7. Hand-feeding may still be needed; smaller frequent meals work best. See our nutrition guide. Mild side effects (soft stools, brief appetite dips, injection-site reactions) are common in this window and usually harmless — see side effects guide for what's normal vs concerning.
Day 5–7: Decision point
By day 5–7, evidence of treatment response should be clear: fever resolved, appetite returning, mild energy increase. If none of these have happened, contact our team. The dose may need to be increased by +2 mg/kg, or the FIP form classification may need revision (eg. wet FIP that's actually mixed wet/dry).
Days 8–10: Visible recovery
By day 8–10 the cat looks visibly better. Wet FIP cats show clear belly-size reduction. Dry FIP cats look more alert, eyes brighter, grooming returning. Injection routine becomes calmer; cat may start anticipating the post-injection treat rather than dreading the injection. Track weight — most cats stabilise or gain 50–150 g in this window.
Days 11–14: Routine settles in
By the end of week 2, the daily protocol becomes a stable habit. Injection takes 2–3 minutes, no struggle. The cat is eating, drinking, mostly playing. Weight is gaining slowly. The first 2 weeks were the hardest — the next 10 weeks are mostly maintenance. Schedule day-28 bloodwork now so it's booked.
Milestones to celebrate
First fever-free morning (usually day 2–3)
First full meal eaten voluntarily (usually day 3–5)
First self-grooming session (usually day 5–7)
First play behaviour returning (usually day 7–10)
First measurable weight gain on the scale (usually day 7–12)
First calm injection without struggle (usually day 10–14)
Warning signs in the first 14 days
Fever still present at day 5 — dose increase may be needed
No appetite improvement by day 7 — consult our team and your vet
New neurological signs appearing — wet/dry FIP may have an underlying neuro component; see neurological FIP guide
Severe vomiting, breathing distress, seizures — emergency vet immediately
Weight loss continuing past day 10 — dose recalculation required
Tracking and logging
Keep a simple daily log for the first 14 days. Date, temperature, weight, dose given (ml and mg), injection site, food intake (poor/normal/good), energy (1–10), notable behaviours. This makes it easy for our team to interpret your case if you contact us, and gives you a clear sense of progress that day-to-day fluctuations can mask.
First bloodwork at day 28 will be the first objective confirmation that treatment is working. See bloodwork guide for what to expect.
Frequently Asked Questions
When can I say treatment is definitely working?
By day 14, if fever has resolved, appetite is restored, and the cat is gaining weight or stable, treatment is working. Day-28 bloodwork is the formal confirmation.
What if my cat seems worse before getting better?
Brief worsening in days 3–5 is not unusual, especially for dry FIP. As long as the cat is eating and not in distress, hold the course. Significant worsening beyond day 7 needs review.
How often should I contact your team in the first 14 days?
As often as you need to. Many owners check in daily for the first week and then taper. See our free consultation guide for when to call.
When can I expect long-term remission?
Sustained remission is declared after the cat completes the full 84-day treatment AND the subsequent 84-day observation period without relapse. Total: 168 days. See survival rate data for what to expect.
Informational only — not veterinary advice. Individual timelines vary; consult your treating vet for case-specific guidance.
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