<prompt> Lovastatin acts by inhibitingHMGCoA reductaseHMGCoA synthetase17- HydroxyalseBile-acid synthetase  <response>: Ans. a HMGCoA reductase. Ref. Harrison Medicine I6thI43I, 2168, 2296, table 335-6HMG-CoA REDUCTASE INHIBITORS HMG-CoA reductase is the rate-limiting step in cholesterol biosynthesis. By inhibiting cholesterol biosynthesis, HMG-CoA reductase inhibitors statins lead to -- increased hepatic LDL receptor activity and accelerated clearance of circulating LDL, resulting in a dose-dependent reduction in plasma LDL-C. HMG-CoA reductase inhibitors are the drug class of choice for LDL-C reduction. They also reduce plasma triglycerides in a dose-dependent fashion, which is proportional to their LDL-C lowering effects . They have a modest HDL-raising effect 5 to 10, and this effect is not dose-dependent. HMG-CoA reductase inhibitors are well tolerated and can be taken in tablet form once a day. Potential Side Effects include:Dyspepsia,- Headaches,- Fatigue,- Muscle or joint pains- Severe myopathy- Rhabdomyolysis rarely.- Hepatitis The risk of myopathy is increased by the presence of renal insufficiency and by coadministration of drugs that interfere with the metabolism of HMG-CoA reductase inhibitors, such as erythromycin and related antibiotics, antifungal agents, immunosuppressive drugs, and fibric acid derivatives. Serum CPK levels do not need to be monitored on a routine basis as an elevated CPK in the absence of symptoms does not predict the development of myopathy and does not necessarily suggest the need for discontinuing the drug.DRUGS USED FOR THE TREATMENT OF HYPERLIPIDEMIADrugMajor indicationsMechanismCommon side effectsHMG-CoA reductase inhibitors statinsElevated LDLCholesterol synthesis;LDL receptors, hepatic VLDLProductionMyalgias, arthralgias, DyspepsiaBile acid sequestrantsElevated triglycerides Bile acid excretion and LDL receptorsBloating, constipation.Nicotinic acidElevated LDL, HDL,Elevated TGVLDL hepatic synthesis and HDL.Cutaneous flushing;GI upset;Elevated glucose, uric acid, levels and liver function tests.Fibric acid derivatesElevated remnants LPL, VLDLDyspepsia myalgia; gall stones. 