Famciclovir Main Uses
Feline Herpesvirus (FHV-1) Treatment: Used to control infections caused by Feline Herpesvirus Type 1 (FHV-1), also known as Feline Viral Rhinotracheitis (FVR), the most common cause of upper respiratory infection in cats.
Upper Respiratory Symptoms: Helps manage FHV-1-associated sneezing, nasal discharge, nasal congestion, and fever.
Ocular Disease: Used to treat FHV-1-associated conjunctivitis, keratitis (corneal inflammation), blepharitis (eyelid inflammation), and corneal ulcers.
Dermatitis: Used in cats with FHV-1-associated skin conditions including eosinophilic or ulcerative dermatitis where the herpesvirus is identified as the underlying trigger.
Off-label use: Famciclovir is a human antiviral medication (brand name Famvir) prescribed by veterinarians in Canada for cats under extra-label provisions. Always follow your veterinarian's specific dosing instructions.
 
Famciclovir Active Ingredients
Famciclovir (prodrug): A synthetic acyclic guanine nucleoside analogue that is pharmacologically inactive on its own. After oral administration, it is converted to its active metabolite, penciclovir, via intestinal and hepatic metabolism.
Penciclovir (active metabolite): A nucleoside analogue DNA polymerase inhibitor. Once phosphorylated by viral thymidine kinase inside FHV-1-infected cells, it competitively blocks viral DNA polymerase, preventing the virus from replicating.
Action Mechanism: Famciclovir does not kill existing virus particles and cannot eliminate the latent herpesvirus reservoir from nerve ganglia. It controls active viral replication, reducing symptoms and viral shedding during active flares.
 
Famciclovir Dosage & Administration
Route: Oral tablet, given by mouth. Dosing is weight-based and must be determined by your veterinarian.
Published dose range: 90 mg/kg orally, every 12 hours (twice daily).
Feeding: Best given on an empty stomach for optimal absorption. If vomiting or GI upset occurs, give with a small amount of food.
Tablet strengths available in Canada: 125 mg, 250 mg, and 500 mg (human formulation dispensed under Canadian DIN). Your veterinarian will prescribe the appropriate strength based on your cat's weight.
Duration: Acute treatment courses commonly range from 3 to 4 weeks. Long-term or episodic use may be prescribed for cats with recurring FHV-1 flares.
Missed dose: Give as soon as remembered. If the next dose is close, skip the missed dose and resume the regular schedule. Do not double-dose.
Kidney impairment: Dose reduction is required in cats with reduced kidney function. Consult your veterinarian.
 
Famciclovir Safety & Side Effects
Generally well tolerated in cats across published clinical studies. Adverse effects are uncommon and include decreased appetite, vomiting, loose stools, and lethargy.
Kidney disease: Penciclovir (the active metabolite) is renally excreted. Use with caution and at reduced doses in cats with chronic kidney disease (CKD). Periodic blood work monitoring is advisable for long-term use.
Hypersensitivity: Do not use in cats with a known allergy to famciclovir, penciclovir, or related drugs.
Drug interactions: Probenecid may increase penciclovir blood levels. Inform your veterinarian of all medications, supplements, or herbal products being given concurrently.
Long-term use: Veterinary reassessment and periodic blood and urine testing are recommended for cats on prolonged famciclovir therapy.
 
Famciclovir Manufacturer Information
Manufacturer: Available in Canada as a generic from Health Canada-approved manufacturers.