Small Animal Clinical Pharmacology - CYF MEDICAL DISTRIBUTION

CLASSES OF DRUGS USED TO TREAT OCULAR INFLAMMATION
Hydrocortisone
Hydrocortisone has the least anti-inflammatory effect
and does not penetrate the cornea well. It is most commonly
used for the treatment of allergic conjunctivitis.
In most cases hydrocortisone either as a drop or an
ointment is not effective in treating uveitis.
Subconjunctival corticosteroids
In animals that are difficult to medicate topically, or
when poor owner compliance is anticipated, depot corticosteroids
can be given by subconjunctival injection,
either under the conjunctiva of the eyeball (epibulbar)
or under the eyelid conjunctiva (subpalpebral). Subconjunctival
injections of corticosteroids are contraindicated
in all cases where corneal ulceration threatens or
is present and when infection is present in either the
cornea or the conjunctiva.
After subconjunctival corticosteroid treatment, owners
should be warned to watch closely for signs of infection
such as increased levels of ocular discharge, blepharospasm,
increased corneal opacification or increased
ocular pain. Unlike topical corticosteroids, it is much
more difficult to withdraw corticosteroids administered
subconjunctivally should an infection or ulcer develop.
If complications occur it is essential to recognize the
problem quickly and if possible, attempt to surgically
remove the residue of the subconjunctival injection.
The use of methylprednisolone by subconjunctival
injection is not recommended as it can be associated
with unsightly granuloma formation following
administration.
Formulations and dose rates
DOGS
Betamethasone dipropionate 5 mg/mL and betamethasone
phosphate 1 mg/mL
• 0.5–1.0 mL subconjunctivally
Dexamethasone phenylpropionate 2 mg/mL and
dexamethasone sodium phosphate 1 mg/mL
• 0.5–1.0 mL subconjunctivally
Dexamethasone-21-isonicotinate 3 mg/mL
• 0.25–1.5 mL subconjunctivally
CATS
Betamethasone dipropionate 5 mg/mL and betamethasone
phosphate 1 mg/mL
• 0.25 mL subconjunctivally
Dexamethasone phenylpropionate 2 mg/mL and
dexamethasone sodium phosphate 1 mg/mL
• 0.25–0.5 mL subconjunctivally
Dexamethasone-21-isonicotinate 3 mg/mL
• 0.1–0.25 mL subconjunctivally
Systemic corticosteroids
Clinical applications
When treating uveitis it is important to treat the posterior
segment of the eye. This requires systemic corticosteroids,
as the other therapeutic routes are unlikely to
reach the target tissue. For example, topical and subconjunctival
therapies are unlikely to be effective for
inflammatory conditions of the optic nerve so systemic
therapy is indicated.
Formulations and dose rates
Prednisolone is the most common corticosteroid used systemically to
treat ocular infl ammation.
DOGS AND CATS
• 1.0–2.0 mg/kg q.12 h for 5 d, then q.24 h for 5 d, then q.48 h
for 10–14 d
The dosage regimen may need to be varied depending on the clinical
response. For longer-term control of infl ammatory ocular conditions,
NSAIDs may be preferred.
Contraindications and precautions
● Ophthalmic corticosteroids (either topical or subconjunctival)
are contraindicated in all cases of
corneal ulceration and any corneal wound or infection.
Systemic corticosteroids at usual doses do not
have much effect on the healing of noninfected
corneal ulcers.
● Corticosteroids are contraindicated whenever there
is any infection inside the eyeball, or in the eyelids.
Adverse effects
Potentiation of corneal ulceration
Topical corticosteroids should never be applied to an
ulcerated cornea, or to a cornea that is likely to ulcerate.
Topically applied corticosteroids can dramatically
worsen corneal ulceration by retarding epithelial healing
and can potentiate collagenases by up to 15 times. Collagenases,
when released in controlled amounts, assist
healing by allowing epithelial cells to slide across the
ulcer bed. However, when mixed with corticosteroids,
collagenase activity is greatly potentiated, resulting in
rapid destruction of normal corneal structure. Clinically
this is seen as a melting cornea. Systemic corticosteroids
at normal doses seem to have no effect on corneal collagenase
activity. However, it would be prudent to use
a systemic NSAID drug rather than a corticosteroid
when treating a melting cornea.
Before using a topical corticosteroid the clinician
should always apply fluorescein stain to check for
corneal ulceration.
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