The results of skin tests in three quinine-sensitive subjects with 42–48 cinchona alkaloids, including several pairs and one quartette of optical isomers, and with some chemically related substances show that the allergic reactions rest on somewhat different chemical bases in all three cases. In the optically isomeric quartette, quinine (ddll), epiquinine (ddld), epiquinidine (dddl) and quinidine (dddd) all three had allergic reactions to quinine that did not appear on administration of quinidine, and judging from skin tests were possibly insensitive to both epialkaloids also.

Results with five of the more common alkaloids in a fourth individual, with coryzal reaction to quinine, are given. Two other subjects, with urticarial reaction to quinine, had no such side effect from quinidine. These subjects with allergic reactions to quinine did not give positive skin scratch reactions to quinine.

A female subject with bleeding from the genital tract as a result of quinine administration was similarly affected by quinidine.

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