CureFIP™ GS-441524 + B12 Injectable 40mg/ml
 
High-Concentration Antiviral With Integrated Cobalamin Support for Large, Severe, and Complex Cases
 
What This Product Is
CureFIP™ GS-441524 + B12 40mg/ml is the highest-concentration formulation in the CureFIP™ injectable range, combining GS-441524 at 40mg/ml with cyanocobalamin (Vitamin B12) at 50mcg/ml. It is designed for FIP cases where two clinical requirements converge simultaneously: the need for high-dose or high-volume antiviral delivery, and the presence of secondary systemic complications that warrant cobalamin support.
 
This convergence is more common than it might appear. The cases that most often require 40mg/ml — large cats, severe presentations, relapse, and high-dose induction — are also the cases most likely to present with systemic debilitation. A 7 kg cat with severe wet FIP and concurrent anaemia, or a large cat relapsing after previous treatment with progressive neurological signs, represents exactly the patient profile this formulation addresses.
 
Why 40mg/ml: The Volume Rationale
Large cats and high-dose protocols produce GS-441524 dose requirements that generate impractical injection volumes at 30mg/ml. The 40mg/ml concentration resolves this by reducing injection volume while maintaining dose accuracy. The full clinical rationale is detailed on the standard 40mg/ml product page — the volume argument applies equally here. The addition of B12 at 50mcg/ml does not alter GS-441524 concentration, injection volume calculation, or antiviral mechanism.
 
Why B12 in the Highest-Concentration Formulation
The cases served by 40mg/ml are disproportionately the most clinically complex in the FIP treatment population. Several factors specific to this patient group make cobalamin support particularly relevant:
 
Large cats have larger absolute B12 requirements. Cobalamin metabolism scales with body mass. A 7 kg cat depleted by systemic illness has a meaningfully larger absolute B12 deficit than a 3 kg cat with equivalent clinical severity. Supplementation at the same concentration delivers proportionally more cobalamin per injection as dose volume increases with weight — a beneficial pharmacokinetic characteristic in this population.
 
Relapse and resistance cases have often been ill longer. Cats reaching retreatment have typically experienced extended illness duration, during which systemic depletion — including B12-dependent haematopoietic and neurological reserves — has progressed further than in first-line cases. Nutritional repletion support is more acutely needed, not less.
 
High-dose induction places greater physiological demand on the cat. During aggressive early dosing phases, the cat is simultaneously managing rapid viral die-off, inflammatory resolution, and the metabolic demands of recovery. Cobalamin support during this period accelerates haematopoietic recovery and reduces the duration of B12-responsive symptoms.
 
Severe presentations have greater secondary complication burden. Severe wet FIP, advanced neurological FIP, and relapse cases present with more extensive systemic damage than standard first-line cases. The full cobalamin support rationale — anaemia support, neurological myelin maintenance, appetite restoration, immune function — applies with greater clinical urgency in this population.
 
Indicated Cases
This formulation is most appropriate for:
Large cats over 5 kg with FIP and concurrent anaemia, neurological involvement, or significant appetite suppression
Severe wet FIP presentations in large cats requiring high-dose induction with simultaneous systemic support
Relapse cases in cats over 5 kg where retreatment involves dose escalation alongside systemic debilitation
Resistance cases requiring escalated dosing in cats with concurrent haematological compromise
Cases where reducing the number of daily injections is clinically or practically important — this formulation consolidates antiviral treatment and B12 supplementation into a single administration
 
This Formulation Is Not the First Choice For
Cats under 5 kg — select the appropriate concentration for the weight range
Cases where the primary concern is systemic support rather than high-dose antiviral delivery — the 30mg/ml + B12 formulation is more appropriate for standard-weight cats with complications
Cases requiring therapeutic-dose B12 supplementation at intervals other than once daily — maintain a separate B12 protocol as directed by your veterinarian
 
Concentration Selection Guide
Concentration
Primary Indication
20mg/ml + B12
Cats under 2.5 kg with systemic complications
30mg/ml + B12
Cats 2.5–5 kg with systemic complications
40mg/ml + B12 (this product)
Cats over 5 kg · High-dose · Severe · Resistance · Relapse + systemic complications
40mg/ml
Same indications · No secondary systemic complications
 
Resistance and Relapse: The Dual Antiviral Consideration
For confirmed GS-441524 resistance or relapse cases, the 40mg/ml + B12 formulation addresses the antiviral dose requirement and systemic support need. However, dose escalation alone may be insufficient in true resistance cases. CureFIP™ Dual Antiviral Oral Capsules (GS-441524 + EIDD-1931) can be used alongside injectable GS-441524 to provide mechanistically distinct dual antiviral coverage — EIDD-1931's lethal mutagenesis mechanism is not subject to the same resistance pathways as GS-441524's chain termination mechanism.
 
If resistance is suspected, contact our clinical support team. Our advisors can help determine whether dose escalation alone, dual antiviral initiation, or a combination approach is most appropriate for your cat's specific case history.
 
Administration
Administer subcutaneously once daily. Dose is calculated in mg of GS-441524 per kg of body weight. The B12 component does not alter the dose calculation. 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.