Fexofenadine is metabolic product of
**Core Concept**
Fexofenadine is a second-generation antihistamine used to relieve symptoms of hay fever and other allergies. Its pharmacological action is mediated through selective histamine H1 receptor antagonism.
**Why the Correct Answer is Right**
Fexofenadine is a metabolic product of terfenadine, another antihistamine that was previously used to treat allergies. Terfenadine undergoes extensive first-pass metabolism in the liver, primarily by the enzyme CYP3A4, to produce fexofenadine. This metabolic pathway is crucial for the elimination of terfenadine from the body, as fexofenadine has a more favorable safety profile compared to its parent compound.
**Why Each Wrong Option is Incorrect**
**Option A:** Loratadine - Loratadine is a second-generation antihistamine in its own right, but it is not the precursor to fexofenadine.
**Option B:** Cetirizine - Cetirizine is another second-generation antihistamine, but it is not metabolically related to fexofenadine.
**Option C:** Diphenhydramine - Diphenhydramine is a first-generation antihistamine, and it is not the precursor to fexofenadine.
**Clinical Pearl / High-Yield Fact**
It's essential to recognize that some antihistamines can cause adverse effects due to their metabolites. For instance, terfenadine's metabolite, fexofenadine, has a lower risk of cardiac arrhythmias compared to its parent compound.
**Correct Answer: C. Terfenadine**