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Feline Herpesvirus Type 1

Feline Herpesvirus Type 1

David J. Maggs, BVSc (Hons), DACVO, University of California, Davis

Pharmacology & Medications

|January 2015|Peer Reviewed

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Feline Herpesvirus Type 1

Famciclovir

Dose: Ideal dose still being established and its safety investigated     

Option: 90 mg/kg PO q8h associated with significant improvement in cats with experimental primary herpetic disease

Option: 40 mg/kg PO q8h produced plasma penciclovir concentrations similar to those achieved with above dose2

  • Also produced tear penciclovir concentrations likely effective against feline herpesvirus type 1 (FHV-1)3

Famciclovir is a prodrug that must be converted to its active metabolite penciclovir, a purine analog with in vitro efficacy against FHV-1.4-6 Because cats are markedly deficient in the enzyme required for this conversion,7 famciclovir metabolism is limited and nonlinear.1,2

Lysine

Dose: 500 mg PO q12h8

  • Must be administered as twice-daily bolus
  • Unsuccessful when 250 or 500 mg administered only once daily to shelter cats9 and when patients permitted ad lib access to diet fortified with lysine10,11

Lysine limits in vitro replication of FHV-1 at high concentrations and with concurrent depletion of arginine12; however, this effect was not seen in media containing physiologic lysine and arginine concentrations.13 In experimental conditions, lysine supplementation may reduce viral shedding in cats latently infected with FHV-114 and clinical signs in cats undergoing primary exposure.8

Clinician's Brief

 

Sketch of structure as depicted by University of California, Riverside laboratory

Cidofovir

Dose: 1 drop of 0.5% ophthalmic solution to affected eye q12h15

  • Do not administer systemically.

Cidofovir is a cytosine analog that creates metabolites with a relatively long tissue half-life, permitting it to be used less frequently than other antiviral drugs16; when applied topically to cats experimentally infected with FHV-1, cidofovir reduced viral shedding and clinical disease.15

Reports showed that cidofovir can be associated with stenosis of the nasolacrimal drainage system components during experimental topical use in humans and rabbits,17,18 but this adverse effect has not been noted in cats.

Trifluridine

Dose: 1 drop of 1% ophthalmic solution to affected eye at least 5 times daily19

  • Do not administer systemically.

Trifluridine is a thymidine analog with in vitro efficacy against FHV-120 and excellent corneal epithelial penetration.21 It often is not well tolerated by cats, likely because of a stinging reaction also reported in humans; no controlled studies assessing its use in cats have been conducted.

Idoxuridine

Dose: In United States, can be obtained from compounding pharmacists only; following forms recommended (do not administer systemically)

Compounded form: 1 drop of 0.1% ophthalmic solution to affected eye at least 5 times daily19

Compounded form: 1/4-inch strip of 0.5% ophthalmic ointment to affected eye at least 5 times daily19

When applied topically to cats experimentally infected with FHV-1, cidofovir reduced viral shedding and clinical disease.15

Like trifluridine, idoxuridine is a thymidine analog with in vitro efficacy against FHV-1.4,20 It was commercially available as an ophthalmic solution or ointment for humans with disease attributable to herpes simplex virus type 1 (HSV-1), is well tolerated by most cats, and seems efficacious in many; however, no controlled studies assessing its use in cats have been conducted.

Vidarabine

Dose: In United States, can be obtained from compounding pharmacists only; following form recommended (do not administer systemically)

Compounded form: 1/4-inch strip of 3% ophthalmic ointment to affected eye at least 5 times daily19

Vidarabine, an adenosine analog with in vitro efficacy against FHV-1,20 affects a different viral replication step than do trifluridine and idoxuridine and thus may be effective in patients with a disease apparently resistant to these drugs; no controlled studies in cats have been conducted.

Acyclovir

Dose: 1/4-inch strip of 0.5% ophthalmic ointment to affected eye at least 5 times daily; not available in the United States22

Acyclovir is a purine analog with relatively low in vitro potency against FHV-14,20,22 and poor absorption following oral administration.23 It is also associated with nephrotoxicity and bone marrow suppression22; therefore, systemic administration is not recommended in cats.

Cats treated topically 5 times daily with acyclovir ophthalmic ointment experienced a median time of 12 days to resolution of clinical signs,22 whereas resolution in cats treated q8h took approximately twice as long and occurred only when therapy was increased to 5 times daily. Toxicity was not seen with topical application.22

Valacyclovir

Dose: Use contraindicated in cats

Valacyclovir, an acyclovir prodrug, enhances acyclovir bioavailability, thereby increasing plasma acyclovir concentrations in cats to levels associated with bone marrow suppression and fatal hepatic and renal necrosis.24 Valacyclovir should never be administered systemically to cats.

Ganciclovir

Dose: No data available for cats

  • In humans, available for systemic (IV, PO), intravitreal, and topical ophthalmic (0.15% gel) administration

Based on current safety and efficacy evidence, the optimal therapy is oral famciclovir 3 times daily.1-3

Ganciclovir, a purine analog, appears to be at least 10-fold more effective against FHV-1 than is acyclovir.4,25 However, in humans this agent is relatively more toxic than other antivirals, and there are no reports on its safety or efficacy in cats; thus, it should not be used systemically in cats at this stage. There are no reports of its topical use in cats.

Closing Remarks

Based on current evidence for safety and efficacy of antiviral drugs in cats infected with FHV-1, optimal therapy appears to be famciclovir given orally 3 times daily.1-3

  • If topical therapy is preferred and owners can administer drugs frequently, then topical idoxuridine is usually well tolerated and often effective.4,20
  • For owners who cannot manage therapy more often than q12h, the only topical antiviral with proven efficacy is cidofovir.15,16
  • Lysine can be useful adjunct therapy in some patients, especially to reduce frequency and severity of recrudescent disease episodes.8-11,14
    • Must be administered q12h, not ad lib with food

FHV-1 = feline herpesvirus type 1

References and Author Information

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