Tissue distribution of dexamethasone in feline ocular structures following single topical application of dexamethasone as an ointment or suspension

Objective To compare the dexamethasone concentration in various structures of the feline eye following a single topical application of dexamethasone as an ophthalmic ointment or suspension. Animals studied Nineteen cats, euthanized due to reasons not related to this study, were selected and their ocular health status evaluated. Selected animals were treated with dexamethasone ointment or suspension. Procedure The concentration of dexamethasone was determined in the following structures of the eye: third eyelid, cornea, aqueous humor, iris, lens, vitreous body, and choroid/retina. The dexamethasone concentration in the eye was measured by radioimmunoassay. The applied amount of dexamethasone was 0.05 mg in 0.05 mL Isopto Dex^® ophthalmic suspension and 0.05 mL Isopto Dex^® ophthalmic ointment, respectively. Cats were treated once with ointment or suspension and were euthanized 3 h or 6 h after treatment. Results At 3 h after topical administration the highest concentrations of dexamethasone were measured in the anterior structures of the eye. The concentrations after application of ointment and suspension were comparable. However, 6 h after administration, the concentrations decreased after administration of suspension and increased further after administration of the ointment, leading to significantly higher concentrations of dexamethasone in the third eyelid, cornea and choroid/retina after treatment with ointment. Conclusion Therapeutically relevant concentrations of dexamethasone after a single topical administration were only achieved in the anterior structures of the eye. Six hours after application there was a substantially higher amount of dexamethasone in the anterior structures of cat eyes treated with ophthalmic ointment compared to ophthalmic suspension.     

Punctal stenosis in 6 dogs following the long‐term use of topical neomycin‐polymyxin B‐dexamethasone

Six dogs were diagnosed with punctal stenosis following the long‐term use of topical neomycin‐polymyxin B‐dexamethasone (NPD). All patients were initially presented for ophthalmic diseases requiring ongoing anti‐inflammatory therapy. Five of the 6 dogs had previously or concurrently been treated with topical anti‐inflammatory medications other than NPD. One patient exclusively received topical NPD prior to the diagnosis of punctal stenosis. The onset of punctal stenosis following therapy with NPD was variable among patients, ranging from 4 months to over 1 year. Diagnosis of punctal stenosis was made based upon the presence of epiphora and visualization of fibrotic tissue over the nasolacrimal puncta.