Dalvastatin is a synthetic HMG-CoA reductase inhibitor developed by Rhône-Poulenc Rorer. Dalvastatin is a prodrug and is itself an inactive lactone. After oral ingestion, the drug is hydrolyzed in vivo to the corresponding beta-hydroxy acid, which is the pharmacologically active form. HMG-CoA reductase is the rate-limiting enzyme in the cholesterol biosynthetic pathway. An active form of dalvastatin inhibits HMG-CoA reductase with IC50 of 3.4 nM. In ex vivo assay, orally administered dalvastatin inhibited cholesterol biosynthesis in rat liver slices with an ED50 value of 0.9. The efficacy of dalvastatin to lower cholesterol was investigated in the clinical trials in the 1990s, but no results were reported.