All of the following antihistaminics can be used topically except:
**Core Concept**
Topical antihistamines are used to treat allergic reactions such as itching, redness, and swelling in the eyes, skin, and mucous membranes. They work by blocking the action of histamine, a chemical released during an allergic reaction.
**Why the Correct Answer is Right**
Topical antihistamines are commonly used to treat conditions such as allergic conjunctivitis, atopic dermatitis, and hives. They are available in various forms, including creams, ointments, and eye drops. The correct answer is a type of antihistamine that is typically used systemically, rather than topically.
**Why Each Wrong Option is Incorrect**
**Option A:** Diphenhydramine is a first-generation antihistamine that can be used topically, particularly in eye drops and creams for itching and allergic reactions. It is not the correct answer.
**Option B:** Loratadine is a second-generation antihistamine that is often used orally for systemic allergic reactions. However, it can also be used topically, particularly in creams and ointments for skin conditions. It is not the correct answer.
**Option C:** Fexofenadine is a second-generation antihistamine that is typically used orally for systemic allergic reactions. It is not commonly used topically and is therefore the correct answer.
**Clinical Pearl / High-Yield Fact**
When choosing an antihistamine for topical use, consider the type of allergic reaction and the location of the reaction. First-generation antihistamines like diphenhydramine may be more effective for severe itching and allergic reactions, but can cause sedation and other systemic side effects.
**Correct Answer:** C. Fexofenadine