Page 1248 - Problem-Based Feline Medicine

1240 PART 15 CAT WITH EYE PROBLEMS

most commonly used. Drops need to be used at than conjunctivitis alone. The recommended dose is
least three to four times daily. 250 mg daily.
● Vidarabine (adenine arabinoside. Vira-A, Parke- ● Topical and/or systemic tetracycline antibacteri-
Davis) interferes with DNA polymerase and may be als are commonly used because of their specific
effective in cases that are resistant to idoxuridine. effect on chlamydial and mycoplasmal organisms
Use q 6–8 h. which may be present together with herpesvirus
● Trifluorothymidine (Viroptic, Glaxo Wellcome) infections.
has the best in vitro effect of all available topical – Tetracyclines have a mild anti-inflammatory effect
agents. Use q 6–8 h. on ocular tissue. They suppress antibody pro-
● Acyclovir (Zovirax ophthalmic ointment, Glaxo- duction and chemotaxis of neutrophils, and
SmithKline) may be the only commercially avail- inhibit lipases, collagenases and prostaglandin
able drug in some countries. The efficacy against synthesis. Research also shows that tetracyclines
FHV-1 has been reported as poor. Use q 6–8 h. exert other pleotrophic properties independent of
● Dilute povidine iodine (diluted 50% in saline) has their antimicrobial activity which include inhibi-
been used, but there is only anecdotal evidence of tion of metalloproteases, blockade of nitrous
its efficacy in clinical situations, and at this strength oxide synthetase (a potent mediator of inflam-
can be very irritating to eyes. matory activity), suppression of tumor progres-
sion, bone resorption and angiogenesis.
Oral antiviral agents include:
● Acyclovir (Zovirax) seems very effective, even at Ocular hygiene is important. Regular cleaning of
doses far below the in vitro ED . The usual dose is infected eyes with poly-ionic eye wash solutions will
50
50 mg/kg, q 6–12 h, but watch for toxic signs of make the cat feel more comfortable and suppress sec-
bone marrow suppression even at this dose. Often ondary bacterial infection.
used in conjunction with oral α interferon and syn-
ergism significantly reduces ED of acyclovir. Prognosis
50
● Valaciclovir (Valtrex, GlaxoSmithKline) is an acy-
clovir prodrug, but rapid absorption of this drug in The prognosis for a full and uneventful recovery of her-
cats appears to make it more readily able to cause petic keratitis is very guarded.
toxicity, especially in sick acutely infected cats. In young cats with very severe corneal symblepharon
● Interferon α: α interferon is a cytokine produced formation it is nearly impossible to create a normal
naturally by leukocytes. It may prevent viral cornea. These cases will have permanent scarring and
spread if given in the very early stages of infec- opacity of the cornea with virtually no vision.
tion in acutely infected cats. Most common regi-
men is a 7-day on/7-day off oral course, which is In adult cats, a chronic recurrent state may develop, and
believed to work by absorption through the oral in these cases the prognosis for permanent recovery is
mucosa and tonsils. Treatment with this drug is guarded.
controversial and dosages vary widely. Systemic Virus replication occurs in the cornea, and although not
courses are also used by giving 10 000 IU SC clinically obvious at the time of infection, this will
twice weekly in conjunction with topical idoxuri- manifest in older cats as a chronic geographic keratitis,
dine or acyclovir. sometimes years after the initial infection.
Other therapies that are used:
● Oral lysine: Lysine has been used in human medi- Transmission
cine to suppress clinical signs of herpes simplex
FHV-1 is a ubiquitous viral organism found all over the
infections. Lysine competes with arginine for incor-
world and is highly infectious.
poration in the viral genome. Arginine is necessary
for the replication of the FHV-1 virus and incorpora- Infection of kittens may occur through direct contact
tion of lysine produces a non-infective virus particle. from a carrier state present in queens. Virus is shed 4–6
It may be more effective in cats with corneal disease weeks after queening.