A 58-year-old Indian male with hypertension and dyslipidemia presents with LDL cholesterol of 180 mg/dL despite dietary modification. The structure marked **B** in the cholesterol synthesis pathway diagram is the rate-limiting enzyme. Which of the following drugs acts on this enzyme to reduce LDL cholesterol and is most effective for cardiovascular mortality reduction in this patient?

Explanation

## Why Atorvastatin is right Atorvastatin is a statin that competitively inhibits HMG-CoA reductase (the enzyme marked **B**), the rate-limiting step of cholesterol synthesis. This inhibition decreases intracellular cholesterol, triggering upregulation of LDL receptors on hepatocytes, which increases LDL clearance from blood. Statins are the most effective LDL-lowering agents and provide proven cardiovascular mortality benefit, both through LDL reduction and pleiotropic effects (anti-inflammatory, plaque stabilization). In Indian populations with high cardiovascular risk, statins are first-line therapy for dyslipidemia (KD Tripathi 9e Ch 45; Harper 32e Ch 26). ## Why each distractor is wrong - **Ezetimibe**: Inhibits cholesterol absorption at the intestinal brush border (NPC1L1 transporter), not the rate-limiting enzyme **B**. It is a second-line agent and does not target HMG-CoA reductase. - **Niacin**: Inhibits lipolysis and VLDL synthesis via GPR109A activation, reducing triglycerides and LDL indirectly. It does not act on the rate-limiting enzyme **B** and is less effective than statins for LDL reduction. - **Fibrate**: Activates PPAR-α to enhance triglyceride metabolism and reduce VLDL. It does not inhibit HMG-CoA reductase and is primarily used for hypertriglyceridemia, not as first-line LDL therapy. **High-Yield:** Statins inhibit HMG-CoA reductase (rate-limiting enzyme) → ↓ intracellular cholesterol → ↑ LDL receptors → ↓ blood LDL; proven cardiovascular mortality benefit in Indian dyslipidemic patients. [cite: Harper 32e Ch 26; KD Tripathi 9e Ch 45]