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  • Effects of action of proparacaine and tetracaine topical ophthalmic formulations on corneal sensitivity in horses.

Effects of action of proparacaine and tetracaine topical ophthalmic formulations on corneal sensitivity in horses.

Journal of the American Veterinary Medical Association (2012-12-12)
Karen L Sharrow-Reabe, Wendy M Townsend
ABSTRACT

To compare the corneal anesthetic effects and duration of action of 2 ophthalmic anesthetic agents in horses. Prospective, randomized masked crossover study. 8 clinically normal adult horses. Corneal sensitivity was determined by measuring each eye's corneal touch threshold (CTT) with a Cochet-Bonnet esthesiometer. Each eye's baseline CTT was recorded prior to anesthetic instillation at 0 minutes and every 10 minutes thereafter for 60 minutes. Each eye was randomly assigned to receive 2 of 4 treatments: 0.5% aqueous proparacaine ophthalmic solution (aqueous proparacaine; 8 eyes); 0.5% aqueous tetracaine ophthalmic solution (aqueous tetracaine; 8 eyes); 0.5% viscous tetracaine ophthalmic solution (viscous tetracaine; 8 eyes); and saline (0.9% NaCl) eyewash solution (8 eyes) as a negative control. There was a 48-hour washout period. Every horse received all treatments. Median baseline CTT of eyes was 4.5 cm (range, 0.5 to 6 cm). Median CTT for saline solution-treated eyes never differed significantly from baseline. The maximum anesthetic effect with the other 3 treatments occurred at 10 minutes. Median CTT of eyes at 10 minutes was 0.5 cm (range, 0 to 2.5 cm) with aqueous proparacaine treatment, 0.25 cm (range, 0 to 2.0 cm) with aqueous tetracaine treatment, and 0 cm (range, 0 to 0.5 cm) with viscous tetracaine treatment. Maximum anesthetic duration was 20 minutes with aqueous proparacaine and aqueous tetracaine treatments and 30 minutes with viscous tetracaine treatments. Treatment of eyes with viscous tetracaine resulted in the greatest decrease in CTT and the longest duration of action, compared with treatment with aqueous proparacaine or aqueous tetracaine.

MATERIALS
Product Number
Brand
Product Description

Sigma-Aldrich
Tetracaine hydrochloride, ≥99%
Sigma-Aldrich
Tetracaine, ≥98% (TLC)
Tetracaine hydrochloride, European Pharmacopoeia (EP) Reference Standard
Supelco
Tetracaine hydrochloride, Pharmaceutical Secondary Standard; Certified Reference Material
Tetracaine for system suitability, European Pharmacopoeia (EP) Reference Standard