This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Endocrinology, Subject name: Pharmacology
Alcaftadine trial used this concentration of drug: 
Select and explain. 
A. 5%, B. 1%, C. 0.25%, D. 2.50%
C: 0.25%
Answer: C: 0.25% 
Explanation: * 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'