About simvastatinstatins, hmg-coa reductase inhibitor, a hypolipidemic agent.mechanism of action of simvastatinit is a precursor lactone converted in to active form in the body which competitively inhibits the conversion of 3-hydroxy-3-methyl glutaryl coenzyme a (hmg coa) to mevalonate. the drug exerts it`s action by specific inhibition of enzyme- 3-hydroxy-3-methyl glutaryl coenzyme a reductase (hmg coa reductase) and reduces cholesterol synthesis up to 50% at therapeutic doses. this results in compensatory increase in low density lipoprotein (ldl) receptor expression in liver which ultimately leads to increased receptor mediated uptake and catabolism of intermediate density lipoprotein(idl) and low density lipoprotein (ldl). it causes dose dependent lowering of ldl cholesterol and reduces hepatic synthesis of very low density lipoprotein (vldl) and lowers plasma triglyceride levels. it increases high density lipoprotein (hdl) levels than other statins.