Vet Guide to Cidofovir® in 2025 🐾

Hello, I’m Dr Duncan Houston, BVSc—founder of Ask A Vet. Today we’re discussing Cidofovir® ophthalmic drops—a potent antiviral solution used in cats (and occasionally horses) to treat eye infections caused by feline herpesvirus‑1 (FHV‑1). This guide covers how it works, dosing, administration, possible side effects, and how to support your cat through treatment with confidence and care. 🐱🩺

📘 What Is Cidofovir®?

Cidofovir is a human antiviral medication that, when compounded into an eye drop solution, is used off-label in veterinary medicine to combat FHV‑1—causing conjunctivitis and keratitis in cats :contentReference[oaicite:3]{index=3}. It's available only via prescription and must be compounded to a 0.5% ophthalmic formulation suited for feline use.

✅ Why Use It?

• Treats FHV‑1 eye infections by disrupting viral DNA polymerase, interrupting viral replication :contentReference[oaicite:4]{index=4}.
• Demonstrated to significantly reduce viral shedding and clinical signs in studies of experimentally infected kittens when used twice daily :contentReference[oaicite:5]{index=5}.
• Often chosen over older antivirals (e.g., idoxuridine, vidarabine) due to efficacy and fewer side effects :contentReference[oaicite:6]{index=6}.

📐 Dosing & Administration

Typical regimen:

• 0.5% cidofovir ophthalmic drops into each affected eye twice daily, as prescribed :contentReference[oaicite:7]{index=7}.
• Administer per your vet’s directions—usually for 7–14 days or until symptoms subside.
• Let at least 5 minutes pass before applying any additional eye medications :contentReference[oaicite:8]{index=8}.
• Use gloves and avoid contact with eye or bottle tip to prevent contamination :contentReference[oaicite:9]{index=9}.

⏱️ Onset & Duration of Effect

Cidofovir begins antiviral action quickly, but visible improvements may take several days. Clinical trials show significant reductions in signs and viral shedding after consistent twice-daily use :contentReference[oaicite:10]{index=10}.

⚠️ Possible Side Effects

• Mild burning, stinging, or redness—especially at higher concentrations :contentReference[oaicite:11]{index=11}.
• Rare cases of superficial keratitis or nasolacrimal duct irritation—usually mild :contentReference[oaicite:12]{index=12}.
• Infrequent systemic effects with topical use; IV injections show significant kidney effects, which aren’t a concern with drop usage :contentReference[oaicite:13]{index=13}.

🧼 Administration Tips

• Warm the dropper in your hand to reduce the shock of cold drops on your cat’s eye.
• Hold the eyelid gently, apply one drop, and allow your cat to blink naturally.
• Wipe away any excess with a clean cloth—don’t let them lick it off :contentReference[oaicite:14]{index=14}.
• Label the bottle with start date and monitor stability—discard if cloudy or discolored :contentReference[oaicite:15]{index=15}.
• Refrigerate if recommended, but allow it to warm slightly before use :contentReference[oaicite:16]{index=16}.

🔗 Interactions & Cautions

• Using corticosteroid eye drops simultaneously may reduce antiviral effectiveness :contentReference[oaicite:17]{index=17}.
• Avoid use in breeding, pregnant/nursing, or kidney-compromised cats due to limited safety data :contentReference[oaicite:18]{index=18}.
• Always disclose other eye or systemic medications to your veterinarian :contentReference[oaicite:19]{index=19}.

🩺 Monitoring & Follow-up

• Schedule follow-ups every 3–7 days to assess healing; vet will check for ulcers and measure tear production/pressure.
• If signs worsen or ulceration occurs, further diagnostics (e.g., fluorescein stain, cytology) may be needed :contentReference[oaicite:20]{index=20}.
• Continue drops for duration advised, even if eyes appear improved, to ensure virus suppression.

❓ FAQs

Can dogs use cidofovir eye drops?

No—cidofovir can irritate or damage canine eyes, and is **not** recommended for dogs :contentReference[oaicite:21]{index=21}.

Is cidofovir better than idoxuridine or vidarabine?

Cidofovir, with a longer intracellular half-life, usually requires only twice-daily dosing—often easier for owners and similarly or more effective :contentReference[oaicite:22]{index=22}.

How long are drops effective after opening?

Disinfected, refrigerated eye drops typically last 7–14 days; discard if cloudy, contaminated, or expired :contentReference[oaicite:23]{index=23}.

Why is cidofovir off-label in pets?

Human-approved for IV use, cidofovir isn’t approved for veterinary ophthalmic use. However, vets may compound it legally for ocular use under extra-label protocols :contentReference[oaicite:24]{index=24}.

📌 Final Takeaways

• Cidofovir ophthalmic drops are a powerful treatment against feline herpesvirus eye infections in cats.
• Typical dose: 0.5% , twice daily, 7–14 days, or until clinical resolution.
• Mild ocular irritation is expected; serious side effects are rare.
• Ensure proper administration, follow-up checks, and observe for complications.
• Off-label use is approved under veterinary supervision—always follow the care plan.

Need help treating your cat’s eye infection or curious if cidofovir is right for them? Download the Ask A Vet app for personalized reminders, follow‑up tools, and 24/7 access to veterinary eye care guidance. Clear eyes, happy cats! 🐾❤️