Mechanism of action of atorvastatin is:-

HMG CoA reductase catalyses the rate limiting step in cholesterol biosynthesis (conversion of HMG CoA to mevalonate). Statins act by inhibiting this enzyme competitively and result in decreased cholesterol synthesis in the liver. As liver requires cholesterol for synthesis of bile acids and steroid hormones, it responds by increasing the uptake of LDL from the plasma. This is done by increasing LDL receptors on its surface. Statins are most powerful LDL lowering agents.