Alcaftadine is used to prevent eye irritation brought on by allergic conjunctivitis. It is a H1 histamine receptor antagonist. It was approved by the U.S. Food and Drug Administration in 2010 under the trade name Lastacaft. Alcaftadine is an antagonist at three of the histamine receptors (1, 2 and 4). The main indication for Alcaftadine is for prevention of allergic conjunctivitis. By blocking these four receptors, Alcaftadine has been shown to significantly reduce the effects of allergens.