Vetdrugs 2.0Famciclovir is an orally administered antiviral prodrug converted to penciclovir. Its principal veterinary application is clinical disease associated with feline herpesvirus type 1, including ocular, respiratory and dermatologic manifestations. It suppresses viral replication during active infection and is used in cats with experimentally induced or naturally occurring herpetic disease.
Group
Antiviral nucleoside analogue
Mechanism of Action
Famciclovir is converted to penciclovir, which is phosphorylated in infected cells to its active triphosphate form. Penciclovir triphosphate inhibits viral DNA polymerase and interferes with viral DNA synthesis, limiting replication of susceptible herpesvirus. Preferential activation in infected cells contributes to antiviral selectivity. The effect is suppressive and does not remove latent virus from infected tissues.
Dose Rates
Cat
| Use / stage | Dose | Route | Schedule | Instructions |
|---|---|---|---|---|
| Feline herpesvirus disease | 90 mg/kg | PO | Every 12 h | |
| Feline herpesvirus disease | 90 mg/kg | PO | Every 8 h | Alternative higher-frequency regimen. |
| Kitten herpesvirus disease | 30–50 mg/kg | PO | Every 12 h | Kittens. |
| Historical fixed herpesvirus regimens | Reference only | PO | Early 62.5 mg/cat regimens produced inadequate exposure. At least 125 mg/cat every 8–12 hours has been used; 500 mg/cat doses are also reported, but weight-dependent examples do not establish a universal fixed regimen. | |
| Feline herpesvirus infection | 125 mg | PO | Every 8–12 h | Alternative older fixed-dose regimen. These alternatives do not establish equivalence to weight-based protocols. |
| Feline herpesvirus infection | 31.25 mg | PO | Every 12 h | Up to 14 days; FHV-1 rhinotracheitis; described course 10–14 days. These alternatives do not establish equivalence to weight-based protocols. |
| Feline herpesvirus infection | 15.625 mg | PO | Every 24 h | Up to 14 days; Kitten-specific historical regimen. These alternatives do not establish equivalence to weight-based protocols. |
| Feline herpesvirus infection | 62.5 mg | PO | Every 24 h | Up to 21 days; Adult-cat historical regimen. These alternatives do not establish equivalence to weight-based protocols. |
Indications
- Treatment of feline herpesvirus-associated conjunctivitis and keratitis.
- Treatment of selected feline herpesvirus-associated upper respiratory disease or rhinosinusitis.
- Treatment of feline herpesvirus-associated ulcerative or other characteristic herpetic dermatitis.
Contraindications
- Reduce exposure in renal impairment; pregnancy safety is unestablished.
Adverse effects
- Mild anemia or hematologic changes reported in limited studies
Preparations
| Preparation | Form | Strength | Route |
|---|---|---|---|
| Famciclovir 125 mg | Tablet | 125 mg / tablet | PO |
| Famciclovir 250 mg | Tablet | 250 mg / tablet | PO |
| Famciclovir 500 mg | Tablet | 500 mg / tablet | PO |
| Famciclovir compounded suspension 100 mg/mL Specified 1:1 Ora-Plus/Ora-Sweet vehicle; refrigerate, shake well, 90-day documented stability. | Oral Liquid | 100 mg / mL | PO |
Monitoring and Administration
Monitor renal function and clinical response. Duration is individualized; courses around 2 weeks are commonly described.
A specified 100 mg/mL Ora-Plus/Ora-Sweet compounded suspension was stable for 90 days refrigerated; shake well. This stability does not extend to every compounded vehicle.