Small Animal Clinical Pharmacology - CYF MEDICAL DISTRIBUTION

OTHER ANTIFUNGALS
ANTIFUNGAL AGENTS
Ocular fungal infections in small animals are rare. They
occur more commonly in horses. Fungal infections are
usually seen after injury to the cornea by vegetable matter
or after prolonged use of a combined antibacterialcorticosteroid
preparation. Fungal infections are characterized
by slowly progressing corneal lesions that are
usually white or yellow in color and unresponsive to
intensive antibacterial therapy. Deep corneal scrapings or
a corneal biopsy are usually required to obtain a positive
culture.
There is very little information in the veterinary literature
on the efficacy of drugs used to treat ocular fungal
infections. Fungi can vary widely in their sensitivity to
drugs so sensitivity testing is always indicated.
There are three main groups of antifungal agents:
polyene antibacterials, pyrimidines and imidazoles.
Other drugs used to treat fungal infections include
iodine and silver sulfadiazine. Ophthalmic applications
for these drugs will be discussed in this chapter. Information
on mechanism of action and pharmacokinetics
can be found in Chapter 9.
POLYENE ANTIBACTERIALS
Natamycin
Natamycin is available in a 5% suspension as an ophthalmic
preparation. The preparation is generally well tolerated
but the suspension may adhere to the ulcerated
cornea. Natamycin has poor ability to penetrate the intact
cornea. It must be administered up to six times daily.
Amphotericin B
Amphotericin B is effective against common systemic
fungal infections such as cryptococcosis and blastomycosis.
It is of limited use in intraocular fungal infections
because it has very poor intraocular penetration through
the cornea and the blood–eye barrier and because of its
systemic toxicity.
Amphotericin can be used as a topical preparation but
can be irritant and may cause toxicity to corneal and
conjunctival epithelium. It is of limited use in the treatment
of keratomycosis because it is not effective against
Aspergillus spp, a common cause of keratomycosis.
PYRIMIDINE DERIVATIVES
Flucytosine
Flucytosine is of limited use in ophthalmic practice
because of its limited efficacy against the filamentous
fungi commonly isolated from keratomycosis.
IMIDAZOLE DERIVATIVES
Miconazole
Miconazole has been used to treat keratomycosis in
animals. A commercially available intravenous preparation
can be used subconjunctivally (5–10 mg q.24 h) as
well as topically (1 drop six times daily). Miconazole is
also available as a dermatological or vaginal cream.
Both preparations appear to be well tolerated by the
cornea.
Ketoconazole
Ketoconazole penetrates the eye well when administered
either topically or systemically. Equine keratomycosis
caused by Aspergillus spp appears to respond well to
ketoconazole. A 1% solution is well tolerated by the eye
after topical administration (one crushed ketoconazole
tablet suspended in artificial tears). Ketoconazole has
been reported to cause cataracts in dogs with long-term
oral therapy.
Fluconazole
Fluconazole is available as an intravenous preparation
and can be administered topically or as a subconjunctival
injection. It has also been administered as an
intracameral injection into the anterior chamber to treat
deep-seated corneal fungal infections.
Itraconazole
Oral treatment with itraconazole is effective in treatment
of experimental fungal keratitis in rabbits. Currently,
there are no data to demonstrate that it is effective
in treatment of keratomycosis in the dog or cat. In the
horse 1% itraconazole with 30% DMSO in an ointment
preparation results in high corneal concentrations of the
drug and is well tolerated. Clinically this combination
seems to have great efficacy in the treatment of fungal
keratitis
OTHER ANTIFUNGALS
Povidone-iodine
Povidone-iodine diluted to a 1% concentration normal
saline has been used in the treatment of equine keratomycosis.
No data regarding its clinical efficacy are
available.
Silver sulfadiazine
The author has found silver sulfadiazine to be extremely
effective in the treatment of keratomycosis. It is avail-
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