FIP antivirals in Spain: legal status and quality
8-month-old female cat with effusive FIP diagnosed at your practice. The next day the owner returns with a GS-441524 product bought online through a social-media group and asks you to supervise the treatment.
What is the most appropriate approach?
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A. Explain that such products are unauthorised and not quality-controlled, prescribe only legally available medicines (via exceptional/cascade prescribing) and still offer clinical and laboratory follow-up of the cat
Correct. Unregulated products may not contain the stated concentration, risking treatment failure or relapse. Your role is to inform, prescribe within the regulations and safeguard the animal's welfare, without leaving it without veterinary care.
B. Refuse to see the cat while she receives that product
Leaving the animal without follow-up worsens its prognosis and solves nothing. You can explain the risks and decline to prescribe unauthorised products without abandoning clinical care.
C. Replace it with aciclovir, an authorised and cheaper nucleoside analogue
Aciclovir acts on herpesviruses, not coronaviruses, and is also toxic to cats. Two drugs being nucleoside analogues does not mean they share the same spectrum.
D. Accept the product without reservation: its concentration is standardised like that of an authorised medicine
Quality control is exactly what these products lack: widely variable concentrations between brands and batches have been described, making safe dosing difficult.
lightbulb Key takeaway
The legal status of FIP antivirals changes over time and between countries: check the current exceptional (cascade) prescribing rules before prescribing. Record in the clinical notes what you tell the owner. If the cat receives an unregulated product, clinical and laboratory follow-up remains essential to detect failure and relapse.
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Updated: October 31, 2026 · Educational content for veterinary professionals. It does not replace current clinical guidelines or the judgement of the attending veterinarian.