A Prospective, Randomized, Double-blind Comparison of Buffered vs Plain Tetracaine in Reducing the Pain of Topical Ophthalmic Anesthesia

• Published in: Academic emergency medicine 2003-05, Vol.10 (5), p.469-470
• Main Author: Weaver, C. S
• Format: Article
• Language: English
• ISSN: 1069-6563; 1553-2712
• DOI: 10.1197/aemj.10.5.469-b

OBJECTIVE: Two to three percent of patients presenting to emergency departments have primary complaints related to the eye. Patients with eye complaints often require topical ophthalmic anesthesia to aid in their physical examination and diagnosis. Tetracaine hydrochloride ophthalmic solution is a commonly used ocular anesthetic agent but patients receiving ocular tetracaine commonly complain of pain upon instillation. This study was conducted to determine if buffering ocular tetracaine hydrochloride from its normal pH of 4.54 to a pH of 7.4 reduces the pain of instillation. METHODS: Prospective, randomized, double-blind, 2-treatment, 2-period cross-over, single center study of healthy volunteers 18 years of age or older. Participants were randomized to receive either two drops of buffered or plain tetracaine in a randomly assigned eye. After a mean wash out period of 24 days (range 7-54) participants returned to have two drops of the other medication instilled in the same eye. The participants recorded the pain of instillation on a 100-mm visual analog scale (VAS) immediately and five minutes after instillation. Adverse events were also recorded at these intervals. The primary outcome measure was the intensity of pain as measured on a VAS immediately after instillation. RESULTS: Sixty persons were enrolled in the study with 100% follow up. Immediately after instillation, the adjusted mean VAS for buffered tetracaine was 29.1 mm while the adjusted mean VAS for plain tetracaine was 16.0 mm. The estimated difference was 13.1 mm (95% CI: 6.9 mm, 19.3 mm). There were no adverse events following the instillation of either solution. CONCLUSION: Buffering of tetracaine hydrochloride significantly increases the pain of its instillation in healthy volunteers suggesting that factors other than pH change may be responsible for the pain reduction reported in other studies of ophthalmic anesthetics.