A prospective, randomized, double-blind comparison of buffered versus plain tetracaine in reducing the pain of topical ophthalmic anesthesia

Study objective: We determine whether buffering ocular tetracaine hydrochloride reduces the pain of instillation. Methods: We conducted a prospective, randomized, double-blind, 2-treatment, 2-period crossover, single center study of healthy volunteers 18 years of age or older. Participants were randomized to receive either 2 drops of buffered or plain tetracaine in a randomly assigned eye. After a mean wash out period of 24 days (range 7 to 54 days), participants returned to have 2 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 5 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 score for buffered tetracaine was 29.1 mm, and the adjusted mean VAS score for plain tetracaine was 16.0 mm. The estimated difference was 13.1 mm (95% confidence interval 6.9 to 19.3 mm). Conclusion: Buffering of tetracaine hydrochloride significantly increases the pain of its instillation in healthy volunteers, suggesting that pain with instillation of ocular anesthetics is not dependent on low pH. [Ann Emerg Med. 2003;41:827-831.]