Which of the following is NOT a second generation antihistaminic ?
**Question:** Which of the following is NOT a second generation antihistaminic?
A. Cetirizine
B. Fexofenadine
C. Loratadine
D. Terfenadine
**Correct Answer:** Terfenadine
**Core Concept:** Second-generation antihistamines are a class of antihistamines that were developed to overcome the limitations of first-generation antihistamines. They are less sedating and have fewer central nervous system (CNS) side effects, making them more suitable for treating allergic conditions.
**Why the Correct Answer is Right:** Terfenadine is a first-generation antihistamine (also known as a "first-generation H1-receptor antagonist"). First-generation antihistamines (e.g., diphenhydramine, promethazine) have stronger CNS effects due to their ability to cross the blood-brain barrier, causing sedation, drowsiness, and impaired psychomotor function.
**Why Each Wrong Option is Incorrect:**
**Option A (Cetirizine):** Cetirizine is a second-generation antihistamine that is highly selective for the H1-receptor and less likely to cause sedation and CNS side effects.
**Option B (Fexofenadine):** Fexofenadine is another second-generation antihistamine with a similar profile to cetirizine, exhibiting less sedation and fewer CNS side effects.
**Option C (Loratadine):** Loratadine is another second-generation antihistamine, providing a similar profile to cetirizine, fexofenadine, and cetirizine, which are less sedating and have fewer CNS side effects.
**Option D (Terfenadine):** As mentioned earlier, Terfenadine is a first-generation antihistamine with strong CNS side effects due to its ability to cross the blood-brain barrier.
**Core Concept:** Second-generation antihistamines are preferred over first-generation antihistamines due to their reduced sedative and CNS side effects. They are more selective for the H1-receptor, minimizing the risk of unwanted side effects.
**Why Each Wrong Option is Incorrect:**
**Option A (Cetirizine):** Cetirizine is a selective H1-receptor antagonist with reduced sedative and CNS side effects.
**Option B (Fexofenadine):** Fexofenadine is another selective H1-receptor antagonist, exhibiting reduced sedation and fewer CNS side effects.
**Option C (Loratadine):** Loratadine is a selective H1-receptor antagonist with reduced sedative and CNS side effects due to its reduced ability to cross the blood-brain barrier.
**Option D (Terfenadine):** Terfenadine is a first-generation antihistamine with strong CNS side effects, as it is not selective for the H