Vet Guide to Famciclovir in 2025 🐾

Greetings—I'm Dr Duncan Houston, BVSc—founder of Ask A Vet. This 2025 guide covers everything you need to know about famciclovir, a potent antiviral used—typically off-label—in cats to combat feline herpesvirus (FHV-1), especially in eye and respiratory cases. Ideal for owners seeking targeted treatment and long-term management strategies. 💊😺

📘 What Is Famciclovir?

Famciclovir is a **nucleoside analog antiviral**—a prodrug that converts to penciclovir in the cat’s body, blocking the virus’s DNA replication mechanism. Though off-label**, it is widely used to reduce FHV‑1 symptoms, viral shedding, and flare-ups :contentReference[oaicite:3]{index=3}.

✅ Uses in Veterinary Medicine

• Feline herpesvirus (FHV-1): Especially useful in ocular (conjunctivitis, keratitis) and respiratory flare-ups :contentReference[oaicite:4]{index=4}.
• Recurrent/chronic cases: Often prescribed for weeks post‑sign remission to protect tear ducts and respiratory tissues :contentReference[oaicite:5]{index=5}.
• Off-label use in dogs or other species: Rare, but possible—always vet-directed.

📐 Dosing & Administration

• Cats: 90 mg/kg orally every 8–12 h—continue for ≥7 days past symptom resolution :contentReference[oaicite:6]{index=6}.
• Typical tablet strengths are 125 mg, 250 mg; dosing via compounding (suspension, paste) is common for precise weight-based dosing :contentReference[oaicite:7]{index=7}.
• Administer on an empty stomach for better absorption—if vomiting occurs, give with food :contentReference[oaicite:8]{index=8}.
• Missed dose? Administer as soon as possible; skip if very close to the next scheduled dose—never double up :contentReference[oaicite:9]{index=9}.

⏱️ Onset & Duration

Famciclovir takes several days to reach full effect, but improvements often begin in 2–5 days. Therapy is typically continued for 1–3+ weeks based on clinical severity :contentReference[oaicite:10]{index=10}.

⚠️ Side Effects & Safety

• Common (often mild): GI upset (vomiting, diarrhea), decreased appetite, increased thirst or urination, lethargy, weight loss :contentReference[oaicite:11]{index=11}.
• In overdose: severe GI signs—seek veterinarian/emergency attention :contentReference[oaicite:12]{index=12}.
• Use with caution in cats with kidney disease; dose adjustment may be required :contentReference[oaicite:13]{index=13}.

🚫 Contraindications & Precautions

• Cats with known hypersensitivity to famciclovir/penciclovir should not receive it :contentReference[oaicite:14]{index=14}.
• Use cautiously in pregnant or nursing cats—risks/benefits must be discussed :contentReference[oaicite:15]{index=15}.
• Ensure hydration and organ function are normal before prolonged therapy :contentReference[oaicite:16]{index=16}.

🔄 Compounding & Formulations

Many cats require compounded forms—liquids, gels, or pastes—due to difficulty in pill administration. These allow accurate dosing and ease of use but may taste bitter and be rejected. Work with your vet to find what works best :contentReference[oaicite:17]{index=17}.

🩺 Monitoring & Follow-Up

• Track appetite, GI signs, hydration, and ocular/respiratory symptoms daily.
• For courses >2 weeks, periodic bloodwork is advised to monitor kidney function and general health.
• Assess response and consider stopping or tapering after 7+ days past clinical resolution :contentReference[oaicite:18]{index=18}.

🏡 Real‑World Example

A 6‑year‑old cat with chronic keratitis and conjunctival discharge was started on famciclovir 90 mg/kg TID. Within 4 days, eye and nasal signs improved. After 3 weeks of therapy and 1 week symptom-free, treatment was tapered and ultimately stopped. No signs recurred in 3-month follow-up.

❓ FAQs

Can dogs take famciclovir?

Occasionally used off-label in dogs—but dose, safety, and effectiveness are less well-studied. Always use under veterinary direction.

What if my cat vomits after dosing?

If within 15‑30 min, re-dose with food. Otherwise, continue as scheduled. Persistent vomiting warrants vet consultation :contentReference[oaicite:19]{index=19}.

How long will therapy last?

Typically 14–28 days—longer in chronic or recurrent cases, with monitoring every 1–2 weeks.

Will it stop future flare-ups?

Famciclovir lowers viral shedding and flare severity, but cannot eradicate latent infection. Repeat courses during flare-ups can reduce severity :contentReference[oaicite:20]{index=20}.

📌 Final Takeaways

• Famciclovir is an effective, veterinarian-prescribed antiviral for cats with FHV‑1 infections.
• Dosage: 90 mg/kg PO every 8–12 h; continue ≥7 days post-resolution.
• Common side-effects are mild; monitor GI and kidney health especially with extended use.
• Compounded forms support palatability and accurate dosing.
• Follow up with symptom tracking and occasional bloodwork; repeat courses as needed. 🐾❤️

Considering famciclovir for your cat? Download the Ask A Vet app for dosage reminders, symptom tracking, vet chat, and chronic disease support—helping your feline friend feel their best in 2025. 😺