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Discomfort and Tetracaine

2006; Elsevier BV; Volume: 113; Issue: 1 Linguagem: Inglês

10.1016/j.ophtha.2005.10.026

1549-4713

Siu Fai Li, Kelly P. Flannigan, Jason B. Lupow,

Ocular Infections and Treatments

Tetracaine is commonly used for topical ophthalmic anesthesia. Unfortunately, it causes discomfort when instilled into the eye.1Bartfield J.M. Holmes T.J. Raccio-Robak N. A comparison of proparacaine and tetracaine eye anesthetics.Acad Emerg Med. 1994; 1: 364-367Crossref PubMed Scopus (55) Google Scholar, 2Shafi T. Koay P. Randomised prospective masked study comparing patient comfort following the instillation of topical proxymetacaine and amethocaine.Br J Ophthalmol. 1998; 82: 1285-1287Crossref PubMed Scopus (23) Google Scholar Although tetracaine typically is stored at room temperature, storage in cold refrigeration is also acceptable.3AHFS Drug Information 1999. American Society of Health-System Pharmacists, Bethesda, MD1999Google Scholar, 4Klasco RK, ed. DrugDex System. Greenwood Village, CO: Thomson Micromedex [edition expires Sep 2005].Google Scholar We wondered if tetracaine would cause less discomfort if it is kept cold. We conducted a crossover trial to compare the pain caused by ophthalmic tetracaine stored at room temperature with that caused by the drug refrigerated. Healthy volunteers were solicited from the emergency department staff by the investigators and included physicians and physician assistants. Informed consent was obtained. The volunteers received 2 drops of tetracaine hydrochloride 0.5% ophthalmic solution (Alcon, Fort Worth, TX) at one temperature in one eye, then were asked to indicate the amount of pain they felt on a 100-mm visual analog scale (VAS).5Todd K.H. Funk K.G. Funk J.P. Bonacci R. Clinical significance of reported changes in pain severity.Ann Emerg Med. 1996; 27: 485-489Abstract Full Text Full Text PDF PubMed Scopus (820) Google Scholar After a period of at least 24 hours, volunteers received 2 drops of tetracaine at the alternate temperature in the same eye and were asked to indicate the amount of pain on a second VAS. In our emergency department, room temperature is generally 66° to 68° F and our refrigerator is 39° to 40° F. One investigator instilled warm tetracaine first, one instilled cold tetracaine first, and the third alternated between the two. The primary outcome of the study was the difference in mean pain scores, as measured by the VAS. Secondary outcomes included the difference in pain scores stratified by the order of tetracaine instillation, and the proportion of volunteers who reported significant differences in pain scores. A difference of 13 mm on the VAS was considered clinically significant.5Todd K.H. Funk K.G. Funk J.P. Bonacci R. Clinical significance of reported changes in pain severity.Ann Emerg Med. 1996; 27: 485-489Abstract Full Text Full Text PDF PubMed Scopus (820) Google Scholar We estimated that 22 volunteers were needed. The study was approved by our institutional review board. Twenty-two volunteers were enrolled; 11 received warm tetracaine first, and 11 received cold tetracaine first. The pain scores reported by the volunteers are shown in Figure 1 (available at http://aaojournal.org). Cold tetracaine was associated with a lower mean pain score (32±24 mm, VAS) compared with warm tetracaine (49±22 mm, VAS). The difference of 17 mm (95% confidence interval [CI], 3–30) was clinically and statistically significant. The intrapersonal differences in pain scores are indicated in Figure 2 (available at http://aaojournal.org). More volunteers favored cold tetracaine than warm tetracaine (59% vs. 9%, respectively; Δ = 50% [95% CI, 26%–74%]). There was little difference in mean pain scores as stratified by the order of tetracaine instillation (38±21 vs. 44±27 mm, VAS; Δ = 6 mm, VAS [95% CI, −9 to 21]).Figure 2Intrapersonal differences in pain scores. VAS = visual analog scale.View Large Image Figure ViewerDownload (PPT) We found the pain of ophthalmic tetracaine instillation was lessened by keeping the medication in refrigeration. Although most volunteers reported less pain with cold tetracaine, it was not unanimous. Two volunteers reported significantly more discomfort with cold tetracaine. The highest pain score overall (83 mm, VAS) was accorded to cold tetracaine. Cold tetracaine may be less painful overall, but it may cause more pain in some individuals. There are several limitations to our study. Assignment of the temperature of the first tetracaine instillation was not random. However, we did not find a difference in pain scores based on the order of the tetracaine instillation. Volunteers were not blinded to the objective of the study (i.e., they knew we were comparing cold and warm tetracaine). We were required by our institutional review board to include this information in our consent document. This may lead to subject bias in the reporting of pain scores. We enrolled healthy volunteers, not patients. Our findings may not be generalizable to the patient population. Finally, we did not assess the duration of discomfort or the efficacy of anesthesia in this study. In summary, refrigeration of tetracaine diminishes the pain associated with topical ophthalmic anesthesia in most healthy volunteers.