Alcaftadine(R89674) is a H1 histamine receptor antagonist, which is used to prevent eye irritation brought on by allergic conjunctivitis. Target: H1 Histamine Receptor Alcaftadine is a broad-spectrum antihistamine displaying a high affinity for histamine H1 and H2 receptors and a lower affinity for H4 receptors. alcaftadine was more effective than placebo and at least as effective as olopatadine 0.01% in preventing ocular itching at 15 minutes and at 16 hours after administration. Alcaftadine 0.025% ophthalmic solution has been approved by the U.S. Food and Drug Administration for prevention of itching associated with allergic conjunctivitis in patients over 2 years of age [1]. Alcaftadine is a safe and effective option for the prevention of ocular itching associated with allergic conjunctivitis, is dosed once daily, and is competitively priced among prescription medications for allergic conjunctivitis [2].