CureFIP™ GS-441524 Injectable 40mg/ml
 
High-Concentration Antiviral for Large Cats, Severe Cases, Resistance, and Relapse
 
What This Product Is
CureFIP™ GS-441524 40mg/ml is the highest-concentration formulation in the CureFIP™ injectable range. It is not a more potent version of the 30mg/ml formulation — the antiviral mechanism and the dose delivered per kg of body weight are identical. The 40mg/ml concentration exists to address a specific clinical problem: delivering an adequate GS-441524 dose in a manageable injection volume when standard concentrations produce volumes that are either excessive or impractical.
 
This formulation serves four primary use cases: large cats whose weight demands high absolute doses, high-dose induction protocols at treatment onset, cases where GS-441524 resistance is suspected and dose escalation is clinically indicated, and relapse cases requiring aggressive retreatment.
 
Why 40mg/ml Is Necessary: The Volume Argument
FIP treatment dose is calculated in mg of GS-441524 per kg of body weight. For a 6 kg cat at a standard dose of 4 mg/kg, the required GS-441524 per injection is 24 mg. At 30mg/ml, this requires 0.8ml — a manageable volume. At higher dose protocols (6–8 mg/kg), the same cat requires 36–48 mg per injection. At 30mg/ml, that becomes 1.2–1.6ml per injection — approaching the upper limit of comfortable subcutaneous administration.
 
At 40mg/ml, the same doses require 0.9–1.2ml — within comfortable range. The 40mg/ml format does not change what the cat receives. It changes the volume in which it is delivered, reducing injection site stress and improving administration practicality at high dose levels.
 
Indicated Cases
Large adult cats over 5 kg Body weight directly determines GS-441524 dose requirement. Cats above 5 kg — Maine Coons, Ragdolls, Norwegian Forest Cats, and large domestic shorthairs — consistently require doses that produce impractical injection volumes at 30mg/ml, particularly at the upper end of standard dosing ranges.
 
High-dose induction at treatment onset Some clinical protocols employ an elevated GS-441524 dose during the first 2–4 weeks of treatment to achieve rapid reduction in viral load before transitioning to standard maintenance dosing. The 40mg/ml formulation is optimised for this induction phase, keeping injection volumes within tolerable limits at elevated dose levels.
 
Suspected GS-441524 resistance Viral resistance to GS-441524 is documented in FIP treatment literature, particularly in cats that have previously received partial or interrupted treatment courses, or that have relapsed following complete treatment. When standard dosing produces insufficient clinical response, dose escalation is a clinically indicated first step before switching agents. The 40mg/ml format makes escalation to 6–8 mg/kg practical without excessive injection volumes.
 
Relapse cases Cats that relapse following completed treatment — particularly within the first 6 months post-treatment — typically require more aggressive retreatment protocols than first-line cases. The 40mg/ml formulation supports the higher dose ranges clinically indicated in relapse management.
 
Severe acute presentations In severe wet FIP, rapidly progressing neurological FIP, and advanced ocular FIP where the treatment window is narrow, aggressive early dosing is clinically justified. The 40mg/ml format enables high-dose initiation from day one of treatment without volume compromise.
 
This Formulation Is Not the First Choice For
Cats weighing under 5 kg at standard dose ranges — the 30mg/ml formulation provides adequate dosing precision
First-line treatment of typical FIP cases in standard-weight cats — 30mg/ml is appropriate and better characterised for this population
Cases where systemic complications (anaemia, neurological involvement) are the primary concern — consider the 40mg/ml + B12 formulation
 
Clinical Background and Resistance Consideration
GS-441524 resistance in FIP treatment has been documented in case reports and small case series, though it remains infrequent in cats completing a full uninterrupted 84-day course at appropriate doses. Resistance risk is highest in cats that received subtherapeutic doses — due to underdosing, treatment interruptions, or low-quality formulations — and in relapse cases.
 
For confirmed or strongly suspected resistance, dose escalation with 40mg/ml is an appropriate first intervention. If escalated monotherapy fails to produce response, transition to dual antiviral therapy with EIDD-1931 (CureFIP™ Dual Antiviral Oral Capsules) — which provides a second, mechanistically distinct antiviral barrier that GS-441524-resistant virus cannot simultaneously overcome.
 
Concentration Selection Guide
Concentration
Primary Indication
20mg/ml
Cats under 2.5 kg · Kittens · Precision dosing
30mg/ml
Cats 2.5–5 kg · Standard FIP · First-line treatment
40mg/ml (this product)
Cats over 5 kg · High-dose · Severe · Resistance · Relapse
40mg/ml + B12
Same as above with concurrent anaemia or systemic complications
 
Administration
Administer subcutaneously once daily. Dose is calculated in mg of GS-441524 per kg of body weight — the concentration change does not alter the dose calculation principle. Standard treatment duration is 84 consecutive days. For high-dose induction protocols, follow veterinary guidance on dose reduction schedule after the induction phase. Use the dosing calculator to determine the correct volume for your cat's current weight and target dose.
 
For relapse or resistance cases, contact our clinical support team before beginning retreatment. Our team can advise on appropriate dose selection and whether dual antiviral therapy should be initiated alongside or instead of dose escalation.