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

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 min post-application. Post-application SPOT scores were recorded immediately following the trial. Linear mixed model statistical analyses (mean ± standard error) were performed (p < .05). RESULTS: Mean eyewash CTT (3.41 cm ± 0.464) was significantly different from ropivacaine-treated (1.44 cm ± 0.562) (p = .008) and lidocaine-treated eyes (1.75 cm ± 0.562) (p = .024); CTT was not significantly different between drug groups (p = .88). Time to maximum anesthesia was not significantly different between ropivacaine (13.25 min ± 3.353) and lidocaine (16.25 min ± 3.353) (p = .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.

Effects of subconjunctival ropivacaine, liposomal bupivacaine, and mepivacaine on corneal sensitivity in healthy horses.

OBJECTIVE: To evaluate corneal sensitivity and adverse events following subconjunctival administration of three local anesthetics in horses. STUDY DESIGN: Randomized, masked, crossover study. ANIMALS: Twelve healthy adult mares. METHODS: The subconjunctival space of the treated eye was injected with 0.2 mL of liposomal bupivacaine (1.3%), ropivacaine (0.5%), or mepivacaine (2%). All horses received each medication once and the contralateral eye received saline (control). Corneal touch threshold (CTT) was measured using a Cochet-Bonnet esthesiometer before sedation, after sedation, and at specified intervals until it returned to baseline. Ocular examinations were performed at 24-, 72, and 168 h post-injection to monitor for adverse effects. RESULTS: The mean total time of anesthesia (TTA) was 168.3 min for ropivacaine, 169.2 min for liposomal bupivacaine, 103.3 min for mepivacaine and 30.7 min for the control. TTA for liposomal bupivacaine (p < .001) and ropivacaine (p = .001) was longer than the control. TTA for mepivacaine was not different from the control (p = .138), liposomal bupivacaine (p = .075) or ropivacaine (p = .150). Injection site hemorrhage reduced TTA regardless of treatments (p = .047). No adverse effects attributed to injections were noted. CONCLUSION: All three medications were well tolerated. Subconjunctival administration of ropivacaine and liposomal bupivacaine resulted in longer TTAs compared to the control; however, their TTAs were not different from that of mepivacaine. CLINICAL SIGNIFICANCE: Subconjunctivally administered liposomal bupivacaine and ropivacaine are viable options to provide prolonged corneal analgesia in horses. Future studies are needed to assess the efficacy in diseased eyes.