Research on Topically Administered Corticosteroids in Horses

Hanneke Hermans, Els M.H. van den Berg, Inge J.M. Slenter, Dax J.C. Vendrig, Lilian L. de Nijs-Tjon, Johannes C.M. Vernooij, Harold Brommer, Michael H. Boevé and Ronette Gehring

Topical dexamethasone and prednisolone are currently the mainstay treatment for equine ophthalmic inflammatory diseases, such as equine recurrent uveitis. Comparative pharmacokinetic studies in horses are lacking and current guidelines are mainly based on empirical data and extrapolation from other species.

New research titled, “Penetration of topically administered dexamethasone disodium phosphate and prednisolone acetate into the normal equine ocular fluids” was authored by Hanneke Hermans, Els M.H. van den Berg, Inge J.M. Slenter, Dax J.C. Vendrig, Lilian L. de Nijs-Tjon, Johannes C.M. Vernooij, Harold Brommer, Michael H. Boevé and Ronette Gehring. You can access this article from BEVA in the Wiley Online Library.

The aim of this prospective randomized experimental pharmacokinetic study was to investigate the penetration and local concentrations of topically applied dexamethasone and prednisolone in normal equine ocular fluids and serum.

Twenty-one Shetland ponies without ophthalmic disease were treated bilaterally topically every 2 hours for 24 hours to obtain steady-state drug concentrations. One eye was treated with 0.15 mg dexamethasone disodium phosphate (0.1%) and the other eye was treated with 1.5 mg prednisolone acetate (1%). Serum samples were taken prior to induction of general anaesthesia. Aqueous and vitreous humour samples were taken during euthanasia at time points after administration of the last dose (t=5min, t=15min, t=30min, t=60min, t=90 min, t=120min, t=180min). Each pony was randomly assigned to one time point and three ponies were sampled per time point. Dexamethasone and prednisolone concentrations were measured by liquid chromatography-mass spectrometry.

The mean ± standard deviation (SD) dexamethasone concentration in aqueous humour was 32.4 ± 10.9 ng/ml and the mean ± SD prednisolone concentration was 321.6 ± 96.0 ng/ml. In the vitreous and in serum samples concentrations of both corticosteroids were below the limit of detection (LOD 2.5 ng/ml).

Bottom Line: Potentially effective dexamethasone and prednisolone concentrations were measured in the anterior chamber, but vitreal concentrations were negligible and systemic uptake was low. Therefore, treatment with only topically administered corticosteroids is deemed insufficient in horses with cases of posterior uveitis.