**Question:** Second generation antihistaminics used in allergic rhinitis are:

A. Cetirizine
B. Loratadine
C. Fexofenadine
D. Desloratadine

**Correct Answer:** D. Desloratadine

**Core Concept:**

Allergic rhinitis is an inflammatory response in the nasal passages triggered by allergen exposure, leading to symptoms such as sneezing, runny nose, and itching. Histamine plays a significant role in this process as it promotes vasodilation, increased vascular permeability, and mucus secretion, contributing to the symptoms of allergic rhinitis.

**Why the Correct Answer is Right:**

Desloratadine is a potent, long-acting second-generation antihistamine that selectively inhibits the action of histamine at H1 receptors, particularly in the nasal mucosa. Unlike older first-generation antihistamines, desloratadine has minimal anticholinergic, sedating, and anti-parkinsonian effects, making it more suitable for treating allergic rhinitis symptoms without causing significant side effects.

**Why Each Wrong Option is Incorrect:**

A. Cetirizine: Similar to desloratadine, it is a second-generation antihistamine with minimal anticholinergic and sedative effects. However, it does not have significant anti-parkinsonian activity, making it slightly less effective than desloratadine in treating allergic rhinitis symptoms.

B. Loratadine: A second-generation antihistamine with minimal side effects, but it also lacks significant anti-parkinsonian activity, making it less effective than desloratadine in treating allergic rhinitis.

C. Fexofenadine: Similar to desloratadine, fexofenadine is a second-generation antihistamine with minimal side effects, but it also lacks significant anti-parkinsonian activity, making it less effective than desloratadine in treating allergic rhinitis symptoms.

**Clinical Pearl:**

Desloratadine is a potent, long-acting, and selective H1 antagonist with minimal side effects, making it a preferred choice for treating allergic rhinitis symptoms. Second-generation antihistamines like desloratadine, cetirizine, loratadine, and fexofenadine share similar pharmacological properties, but their anti-parkinsonian activity is significantly lower than desloratadine. This results in a greater effectiveness in managing allergic rhinitis symptoms.