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To the Editor:
—Since there has been some interest in the use of the antihistamine drugs locally in the eye, the following data on the ocular tolerance to a group of these compounds, which are reported to have particularly high antihistamine activity, may be of use to persons contemplating therapeutic trials.The approximate maximum concentrations at which no alteration of the rabbit cornea occurs, as shown by examination with the slit lamp, after application of a single drop of solution are: phenazoline hydrochloride ("antistin hydrochloride," Ciba Pharmaceutical Products, Inc.), 1.5 per cent; diphenhydramine hydrochloride ("benadryl hydrochloride," Parke, Davis & Company), 1 per cent; doxylamine succinate ("decapryn," Wm. S. Merrell Company), 5 per cent; thenylpyramine hydrochloride ("histadyl," Eli Lilly & Co.), 5 per cent; pyranisamine maleate ("neoantergan," Merck & Co., Inc.), 5 per cent; tripelennamine hydrochloride ("pyribenzamine hydrochloride," Ciba Pharmaceutical Products, Inc.), 2.5 per cent; thenylpyramine hydrochloride ("thenylene," Abbott Laboratories), 5