News Notes

Topical Steroids May Not Be Enough for Some Uveitis

Although equine ophthalmic inflammatory diseases are often treated with topical anti-inflammatory drugs, they might not be good choices for acute equine recurrent uveitis (ERU).

Researchers from Utrecht University, in The Netherlands, found that concentrations of topical dexamethasone (DEX) and prednisolone (PRED) in the vitreous were negligible. In addition, systemic absorption was minimal. Therefore, just treating with topical products might not be sufficient for horses with posterior uveitis.

ERU is a common ophthalmic condition in horses throughout the world. In the United States, for example, the prevalence can be as high as 25%, and in Europe, the prevalence is estimated to be between 7% to 10%. The condition is often debilitating, and despite intensive medical and surgical treatment, ERU eventually leads to blindness in most horses, according to the researchers.

However, treatment typically depends on empiric data and extrapolation of data about treatment in other species because comparative pharmacokinetic data about these topical treatments in horses are limited. They wanted to know how these products worked for horses, so they did a prospective, randomized experimental pharmacokinetic study to look at the penetration and local concentrations of topically applied dexamethasone and prednisolone.

They monitored the equine ocular fluids and serum in 21 Shetland ponies while receiving topical doses of dexamethasone and prednisolone. The horses did not have ophthalmic disease and were slated for euthanasia for another reason.

The horses received topical steroids every 2 hours for 24 hours, which would mimic the type of aggressive treatment a veterinarian would prescribe if the horse had an acute ERU. One eye received 0.15 dexamethasone disodium phosphate (0.1%) and the other eye received 1.5 mg prednisolone acetate. Which eye received which product was chosen randomly.

The researchers took serum samples prior to induction of general anesthesia. Aqueous and vitreous humor samples were taken during euthanasia at various times after administration of the last dose (5 min, 15 min, 30 min, 60 min, 90 min, 120 min and 180 min). Each pony was randomly assigned to 1 time and 3 ponies were sampled per time point.

The mean standard deviation (SD) of dexamethasone concentration in aqueous humor was 32.4 ± 10.9 ng/mL and the mean ± SD prednisolone concentration was 321.6 ± 96.0 ng/mL.

The vitreous and serum concentrations of both corticosteroids were below the limit of detection (LOD 2.5 ng/mL), the researchers said.

“According to current literature, prednisolone acetate has a better ocular penetration than dexamethasone phosphate solutions,” the researchers wrote. “This was not supported by the results of our study. In our study, the penetration of DEX and PRED were not statistically different.”

Administering medication by oral or subconjunctival routes might be better if the horse has recurrent uveitis, they said.

For more information:

Hermans H., van den Berg EMH, Slenter IJM, et al. Penetraion of topically administered dexamethasone disodium phosphate and prednisolone acetate into the normal equine ocular fluids. Equine Vet J. 2021 Oct 27. https://doi.org/10.1111/evj.13526 https://beva.onlinelibrary.wiley.com/doi/10.1111/evj.13526