<prompt> Alcaftadine trial used this concentration of drug:510.252.50  <response>: ALCAFTADINE is a H1 receptor antagonist, and can be used for allergic conjunctivitis The trial done for alcaftadine used 0.25 solution. The trial states: When Alcaftadine was tested against placebo and olopatadine, only Alcaftadine 0.25 was shown to have a clinically significant reduction in conjunctival redness scores 7 and 15 minutes after administration 