Therapeutic Class: Anti-viral
Species: Cats
May Be Prescribed For: Herpes virus infection
Basic Information
Famciclovir is a prodrug that is used to treat herpes virus infections in humans and cats. Famciclovir is converted into penciclovir through a two-step process in the blood and in the liver. Penciclovir inhibits herpes virus DNA synthesis. The half-life of penciclovir in a herpes-infected cell is considerably longer than the half-life in plasma. Famciclovir/penciclovir is virostatic, not virucidal.
Oral famciclovir is well-absorbed by humans. The absorption and blood levels are much more variable in the cat. This is thought to be due to either poor intestinal absorption or a lack of the appropriate hepatic enzyme for the conversion of famciclovir to penciclovir.
Cats
Despite the complex pharmacokinetics of famciclovir/penciclovir, recent studies have demonstrated that the oral administration of famciclovir "improved outcomes for systemic, ophthalmic, clinicopathologic, virologic, and histologic variables in cats experimentally infected with FHV-1." (Thomasy et al. 2011) Earlier work by Malik et al. in 2009 showed improvement in ocular, sinus, and dermatologic manifestations in cats with clinical FHV-1 that were treated with famciclovir.
Side Effects
Famciclovir appears to be well-tolerated in cats. Side effects in humans are mostly related to the GI tract.
Precautions
Famciclovir should be used with caution and at a reduced dose in patients with poor renal function.
Work in laboratory animals has shown that famciclovir is excreted in maternal milk. It is not known if this is of clinical significance in the cat.
Drug Interactions
Concurrent use of famciclovir and probenecid may increase blood levels of penciclovir.
Overdose
Overdose with penciclover can be treated with hemodialysis.