INTRODUCTIONAtorvastatin, a member of a lipid-lowering family ofagents called statins, is a synthetic reversible inhibitor of3-hydroxy-3-methylglutaryl-coenzyme A (HMG-CoA)reductase; the rate-limiting enzyme in cholesterol biosynthesis.This HMG-CoA reductase inhibitor can efficientlyand dose dependently lower both cholesterol(25% to 61%) and triglyceride (9% to 61%) levels inhyperlipidemic patients,1,2 and produces a significantlylarger reduction (38% to 51%; P ≤ 0.01) of cholesteroland triglycerides compared with the equivalent dosesof other statin drugs.3 It has also been reported to reducethe levels of LDL, apolipoprotein B, and intermediatedensitylipoprotein.4 Atorvastatin calcium, in tabletform, is indicated as an adjunct to diet for the preventionof cardiovascular disease and for the treatment ofpatients with hypercholesterolemia, primary dysbetalipoproteinemia,or other forms of dyslipidemia. It isalso used to reduce the risk of myocardial infarction,stroke, and heart failure in people with type 2 diabeteswithout evidence of heart disease.5,6Atorvastatin is highly soluble and permeable in theintestine and it can be rapidly and completely (≥80%)absorbed when administered orally as a calcium salt,with maximum plasma concentration occurring within0.5 to 1.5 hours.7 The oral bioavailability of the parentatorvastatin is ~14% due to presystemic clearance ingastrointestinal mucosa and hepatic first-pass metabolism.7Atorvastatin is extensively metabolized in both thegut wall and liver. Its metabolic pathway is complex,involving cytochrome P450 (CYP) 3A4-mediated oxidationthat leads to at least 2 active metabolites,8 orthohydroxy-atorvastatin(which is the dominant metabolitedetected in plasma) and para-hydroxy-atorvastatin(whose plasma concentration is low),9–11 β-oxidation,lactonization, hydrolysis, and upper gastrointestinalmediatedglucuronidation. Atorvastatin, as well as someof its metabolites (eg, ortho-hydroxy-atorvastatin), ispharmacologically active in humans and ~70% of thetotal circulating inhibitory activity for HMG-CoA reductaseis attributed to these active metabolites.7,9Atorvastatin and its metabolites are eliminated primarily(70% to 80%) in bile following hepatic and extrahepaticmetabolism.7 The plasma clearance of atorvastatin is~625 mL/min and the mean elimination t1/2 in humansis ~7 hours, but the t1/2 of inhibitory activity for HMGCoAreductase is 20 to 30 hours, due to the contributionof active metabolites. The renal route is of minor importance(<1%) for the elimination of atorvastatin.7Although the pharmacokinetics or bioavailability ofatorvastatin has been previously studied in other populations,12–15a search of the MEDLINE and ScienceDirectdatabases in English, including all possible publicationyears, using the terms atorvastatin, ortho-hydroxyatorvastatin,bioequivalence, bioavailability, pharmacokinetic,and Chinese, did not identify published informationon the pharmacokinetics of atorvastatin ina Chinese population, and regulatory requirementsnecessitate a bioequivalence study for the marketing ofa generic product in China. Therefore, the aim of thepresent study was to assess the pharmacokinetics andbioequivalence of a test (Lek Pharmaceuticals d.d.,Ljubljana, Slovenia) and branded reference* formulationof atorvastatin calcium 10-mg tablets after administrationof a 20-mg oral dose in healthy fasted Chinese malevolunteers.
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