**Question:** The non sedative antihistamines are all EXCEPT one:

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

**Core Concept:** Non-sedative antihistamines are a class of medications used for treating allergic symptoms without causing drowsiness or sedation. They primarily target histamine H1 receptors, reducing allergy symptoms like itching, sneezing, and runny nose.

**Why the Correct Answer is Right:**

The correct answer, **Fexofenadine**, is an antihistamine that primarily targets histamine H1 receptors, but it is known to possess sedative properties. This means that fexofenadine can cause drowsiness and sedation, making it an exception to the group of non-sedative antihistamines.

**Why Each Wrong Option is Incorrect:**

A. Cetirizine (H1 receptor antagonist) and Loratadine (H1 receptor antagonist) are non-sedative antihistamines, making them incorrect options.
B. Desloratadine (H1 receptor antagonist) is also a non-sedative antihistamine, hence incorrect as an option.

**Why the Correct Answer is Right:**

Antihistamines like Cetirizine, Loratadine, Desloratadine, and Fexofenadine are all H1 receptor antagonists, blocking the action of histamine at H1 receptors in the body. However, Fexofenadine demonstrates sedative effects due to its pharmacological properties, making it the exception to the group of non-sedative antihistamines.

**Why Each Wrong Option is Incorrect:**

Option A (Cetirizine and Loratadine) and Option B (Desloratadine) are non-sedative antihistamines, making them incorrect choices. Fexofenadine is the correct answer as it is a sedative antihistamine and not part of the non-sedative group.

**Clinical Pearl:** When using antihistamines for treating allergic symptoms, it is important to consider the potential side effects of drowsiness and sedation, especially when prescribing to patients with driving or operating machinery responsibilities.