Correct Answer: A

Rationale: Atorvastatin, a statin class drug, competitively inhibits HMG-CoA reductase, the key enzyme in hepatic cholesterol biosynthesis. This inhibition lowers intracellular cholesterol levels, upregulates LDL receptors on hepatocytes, and increases clearance of circulating LDL from the plasma. The reduction in total cholesterol from 6.8 to 4.3 mmol/L demonstrates effective lipid-lowering therapy. Statins do not primarily act by increasing bile acid excretion or activating lipoprotein lipase, though secondary metabolic effects may occur. This mechanism underlies their role in cardiovascular risk reduction.

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