Topical ropivacaine hydrochloride 0.5% and lidocaine hydrochloride 2% significantly reduce corneal sensitivity without short-term negative side effects in horses.

Abstract

OBJECTIVE: To evaluate corneal sensitivity and acute side effects following application of ropivacaine hydrochloride 0.5% and lidocaine hydrochloride 2% on the healthy equine cornea. ANIMALS STUDIED: Eight healthy adult horses. PROCEDURE: A randomized, masked, crossover study design was utilized. Baseline Semiquantitative Preclinical Ocular Toxicology (SPOT) scores and corneal touch thresholds (CTT) using a Cochet-Bonnet esthesiometer were recorded and measured, respectively, for eight healthy adult horses before medication application. Commercially available eyewash was used as a negative control. Ropivacaine hydrochloride 0.5% or lidocaine hydrochloride 2% solution was sprayed on a randomly selected eye, and the contralateral eye received eyewash. CTT was measured in both eyes at 1, 5, 15, 25, 35, 45, 55, 65, and 75&#x2009;min post-application. Post-application SPOT scores were recorded immediately following the trial. Linear mixed model statistical analyses (mean&#x2009;&#xb1;&#x2009;standard error) were performed (p&#x2009;<&#x2009;.05). RESULTS: Mean eyewash CTT (3.41&#x2009;cm&#x2009;&#xb1;&#x2009;0.464) was significantly different from ropivacaine-treated (1.44&#x2009;cm&#x2009;&#xb1;&#x2009;0.562) (p&#x2009;=&#x2009;.008) and lidocaine-treated eyes (1.75&#x2009;cm&#x2009;&#xb1;&#x2009;0.562) (p&#x2009;=&#x2009;.024); CTT was not significantly different between drug groups (p&#x2009;=&#x2009;.88). Time to maximum anesthesia was not significantly different between ropivacaine (13.25&#x2009;min&#x2009;&#xb1;&#x2009;3.353) and lidocaine (16.25&#x2009;min&#x2009;&#xb1;&#x2009;3.353) (p&#x2009;=&#x2009;.40). No side effects were appreciated as confirmed by SPOT. CONCLUSIONS: Ropivacaine and lidocaine similarly decreased corneal sensitivity when applied topically without clinically evident short-term ocular side effects. Lidocaine may be preferable in clinical settings due to its large, multi-use vials and similar effects to ropivacaine.