Famciclovir

**Famciclovir** is an oral antiviral medication primarily used in veterinary medicine to treat **feline herpesvirus-1 (FHV-1)** infections. * It is a prodrug that is converted in the body to its active antiviral form, **penciclovir**. * Because cats have very low levels of **hepatic aldehyde oxidase** (the enzyme responsible for this conversion), they often require significantly higher doses compared to humans or other species to achieve therapeutic concentrations. * It appears to be well-tolerated for short-term use (2-3 weeks) in cats, though long-term safety data is still limited. * **Clinical Pearl**: While relatively expensive, the availability of generic formulations has made this a more accessible option for severe or refractory FHV-1 cases.

กลไกการออกฤทธิ์: Famciclovir is a prodrug that undergoes biotransformation to become active: Famciclovir → **hepatic aldehyde oxidase** → Penciclovir Once inside a virus-infected cell: Penciclovir → **viral thymidine kinase** → Penciclovir monophosphate → **cellular kinases** → Penciclovir triphosphate * The triphosphate form competes with deoxyguanosine triphosphate to inhibit **herpes virus DNA polymerase**. * This selectively and effectively halts **herpes viral DNA synthesis** and replication. * Viral resistance can occur via mutation.

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