Which is NOT a 2nd generation antihistaminic?
**Core Concept**
The question requires understanding of the classification and pharmacological properties of antihistamines, specifically the distinction between first, second, and third-generation antihistamines. **Second-generation antihistamines** are known for their selectivity towards peripheral H1 receptors, reduced sedative effects, and improved safety profile.
**Why the Correct Answer is Right**
The correct answer will be a drug that does not belong to the second-generation antihistamines due to its pharmacological properties or receptor affinity. Second-generation antihistamines like **Loratadine** and **Fexofenadine** exhibit minimal central nervous system penetration and are less likely to cause sedation.
**Why Each Wrong Option is Incorrect**
**Option A:** Loratadine is a second-generation antihistamine with a selective peripheral action and minimal sedation.
**Option B:** Fexofenadine is another second-generation antihistamine that is less sedating and more selective for peripheral H1 receptors.
**Option C:** **Diphenhydramine** is a first-generation antihistamine known for its significant sedative effects and central nervous system penetration, making it a poor choice for patients with sedation risks.
**Option D:** **Cetirizine** is a second-generation antihistamine with a relatively selective peripheral action and minimal sedation, similar to other second-generation antihistamines.
**Clinical Pearl / High-Yield Fact**
When choosing an antihistamine, remember that first-generation antihistamines like Diphenhydramine are more likely to cause sedation and should be avoided in patients with sedation risks.
**Correct Answer:** C. Diphenhydramine is a first-generation antihistamine.