Suppressive effects of oral ketotifen on skin responses to histamine, codeine, and allergen skin tests.

Nine healthy subjects were given 1 mg ketotifen orally and were skin tested with histamine (4, 10, and 20 micrograms/mL), codeine (0.001%, 0.01%, and 0.1%) and normal saline at varying time intervals up to 96 hours. Seven subjects allergic to tree and dust allergens were studied in the same way and were skin tested with both allergens. The suppression of skin responses in both studies occurred maximally between 4 and 24 hours, and did not disappear until 72 hours. The control subjects not taking ketotifen did not show any suppression. These results suggest that oral ketotifen should be withheld for 72 hours prior to immediate type hypersensitivity skin tests.