Pimecrolimus and sirolimus
Two other drugs, pimecrolimus and sirolimus, are under investigation for use as lacrimostimulants.4,5 However, little is known about their clinical efficacy or safety.
Although they are not new, you may be unfamiliar with topical fluoroquinolones available for use in people, such as 0.3% ofloxacin,
0.3% norfloxacin, 0.3% gatifloxacin, and 0.3% ciprofloxacin. None of these medications should be used for routine antimicrobial
prophylaxis; however, these topical fluoroquinolones can be effective in treating infected corneal ulcers or stromal abscesses,
particularly infections involving gram-negative organisms.
To treat these infections, topical fluoroquinolones should be applied six times daily until the infection resolves. Fluoroquinolones
are effective against Pseudomonas species and Escherichia coli; Staphylococci species are also often susceptible. Fluoroquinolones are usually not recommended to treat Streptococci species infections because those bacteria demonstrate variable susceptibility to fluoroquinolones. Gatifloxacin, ofloxacin,
and ciprofloxacin all penetrate an intact corneal epithelium; however, gatifloxacin offers the best penetration.6-8 The only other topical antibiotic capable of penetrating intact corneal epithelium is chloramphenicol, which is infrequently
used because, though rarely, it can cause aplastic anemia in people.
Antivirals that are now available include idoxuridine, trifluridine, cidofovir, famciclovir, and lysine.
Idoxuridine and trifluridine
Idoxuridine and trifluridine are available as topical antiviral drugs. Both are nucleoside analogues, structurally similar
to the nucleosides used in viral and host DNA and RNA synthesis. Their substitution into viral DNA disrupts the virus replication
Idoxuridine must be compounded and is typically used as a 0.1% solution. One drop is applied four to six times daily for one
week past the resolution of clinical signs. While it is fairly efficacious, some irritation (blepharospasm and redness) may
Trifluridine is available commercially for use in people as a 1% solution. Apply one drop four to six times daily for one
week past the resolution of clinical signs. Trifluridine has excellent in vitro activity against feline rhinotracheitis virus
(FHV-1) but is often not well-tolerated by patients.9 For example, it may cause ocular irritation and a stinging sensation upon application. Moreover, trifluridine costs about
$100 for a 7.5-ml bottle.
With either drug, the required frequent application often leads to poor owner compliance and undue stress for the patient.
In a 0.5% solution, cidofovir, an acyclic analogue of cytosine,9 decreases clinical signs of FHV-1 infection when administered topically twice daily.10 The drug also causes little irritation.10 The lack of irritation and decreased frequency of administration make compliance much easier than treating with idoxuridine
or trifluridine. Cidofovir must be compounded for ophthalmic use.
Systemic antivirals may be required for animals that resist topical application or for those cats with dermatologic or other
systemic signs related to FHV-1 infection. Famciclovir (Famvir—Novartis) is a new oral antiviral medication that shows promise
in cats. At a dosage of 90 mg/kg given orally three times a day for 21 days, no signs of toxicosis were reported, and the
treated cats had significantly lower clinical disease scores than the untreated cats had.11 Anecdotally, some practitioners are administering 1/8 to ¼ of a 125-mg tablet of famciclovir once daily and seeing an improvement
in clinical signs.