Final answer:
For accurate allergy testing, antihistamines like fexofenadine and desloratadine should be discontinued because they block the natural histamine response that needs to be measured during the test.
Step-by-step explanation:
When preparing for allergy testing, it is important to discontinue certain medications that can affect test results. Among the options provided, fexofenadine and desloratadine are antihistamines, which work by preventing histamines released by mast cells from stimulating the itching and swelling of body tissues. Montelukast is an antileukotriene, and beclomethasone is an anti-inflammatory steroid. However, it is specifically the antihistamines—Fexofenadine (B) and Desloratadine (D)—that should be discontinued, as they could prevent an accurate assessment of allergic reactions during testing by blocking the natural histamine response. In the context of this question, fexofenadine and desloratadine would be the correct medications to stop before allergy testing.