Antiviral Therapy

Question 1

Are antivirals used to treat herpesvirus infections efficacious against active infections, latent
infections, or both?

Answer 1

Only actively replicating viruses are inhibited

- not effective against latent infection

Question 2

Due to low oral bioavailability and side‐effects of acyclovir, what antiherpes drugs are
instead used in small animals and horses, respectively.

Answer 2

• dogs and cats: famciclovir (oral prodrug converted to penciclovir)
• horses: valacyclovir (oral prodrug converted to acyclovir) is contraindicated in cats due to severe lethargy, dehydration, leukopenia

Question 3

Be able to recognize the three ophthalmic antiherpes drugs along with their relative merits
as to how well they are tolerated and the frequency of application required.

Answer 3

• trifluridine (1% solution): commercially available, topically q4-6 hrs (stings)
• idoxuridine (0.1% solution or 0.5% ointment): compounded, topically q4-6 hrs (well tolerated)
• cidofovir (0.5% solution): compounded, topically q12 hrs

Question 4

How is oral lysine supplementation proposed to work in decreasing the number of outbreaks and severity of herpesvirus infections in cats?What is its relative safety and
efficacy?

Answer 4

Lysine acts as a competitive inhibitor of arginine during assembly of viral nucleocapsid

• dietary supplementation of L-lysine, coupled with low arginine diet, reduced clinical signs of HSV-1
• very safe, inexpensive
• efficacy is questionable (restriction of arginine is not possible due to essential amino acid status in cats)

Question 5

Oseltamivir (Tamiflu®) is effective on what two types of viruses?

Answer 5

Influenza and parainfluenza

- neuraminidase inhibitors prevent release of new virions and their spread from cell to cell

Question 6

What are the general recommendations on the use of Oseltamivir (Tamiflu®) to treat canine
influenza?

Answer 6

Not recommended for use in vet med due to unknown efficacy

- concerns exits regarding promoting resistance to drugs

Question 7

What evidence supports or refutes the use of Oseltamivir (Tamiflu®) in canine parvovirus
infections?

Answer 7

Evidence indicates it is ineffective
- does not result in significant decrease in hospitalization, treatments needed, clinical scores, morbidity, or mortality

Question 8

What species types of recombinant interferon are available in the USA versus Europe?

Answer 8

• USA: human recombinant IFN-alpha, beta, and gamma

- Japan, Australia, Europe: recombinant feline IFN-w (omega)

Question 9

What is the major limitations of the use of human recombinant interferon in animals?

Answer 9

When given parenterally to cats, human IFN-alpha becomes ineffective after 3-7 weeks due to development of neutralizing antibodies (antigenetically dissimilar)
- cost prohibitive in USA

Question 10

What is the most common CBC side‐effect when using zidovudine (AZT) in cats?

Answer 10

Bone marrow suppression is common, but tolerable

• discontinue if PCV <20%
• resistance to AZT may develop in 6 months