The microsomal enzyme involved in the metabolism of omeprazole is
**Core Concept**
Omeprazole is a proton pump inhibitor (PPI) that requires metabolic activation to exert its anti-secretory effects. Its metabolism involves the action of specific microsomal enzymes in the liver.
**Why the Correct Answer is Right**
The correct answer is CYP2C19, which is a member of the cytochrome P450 enzyme family. CYP2C19 is responsible for the hydroxylation of omeprazole to its active metabolite, which then inhibits the H+/K+ ATPase pump in the gastric parietal cells. This results in a decrease in gastric acid secretion and relief of symptoms in patients with gastroesophageal reflux disease (GERD). CYP2C19 is a polymorphic enzyme, and variations in its gene can lead to different metabolic phenotypes, including poor, intermediate, extensive, and ultrarapid metabolizers.
**Why Each Wrong Option is Incorrect**
* **Option A:** There is no evidence to suggest that CYP3A4 is involved in the metabolism of omeprazole.
* **Option B:** CYP1A2 is involved in the metabolism of several drugs, but it is not the primary enzyme responsible for omeprazole metabolism.
* **Option D:** CYP2D6 is a member of the cytochrome P450 enzyme family, but it is not involved in the metabolism of omeprazole.
**Clinical Pearl / High-Yield Fact**
Patients who are poor metabolizers of CYP2C19 may require lower doses of omeprazole to avoid excessive inhibition of the H+/K+ ATPase pump and increased risk of side effects such as diarrhea and abdominal pain.
**Correct Answer:** C. CYP2C19