Pharmacodynamics and Pharmacokinetic-Pharmacodynamic Relationships of Atorvastatin, an HMG-CoA Reductase Inhibitor

The objective of this study is to determine the relationships between plasma atorvastatin concentrations, LDL (low-density lipoprotein) cholesterol reduction, and atorvastatin dose; the earliest time at which lipid levels change when atorvastatin treatment is initiated or discontinued; and alterations in LDL particle composition. Twenty-four subjects with elevated LDL-cholesterol were treated with escalating daily doses of 5, 20, and 80 mg atorvastatin for 6 weeks each. Serial plasma lipid and lipoprotein analyses were performed during the initiation and discontinuation of atorvastatin therapy, as well as at steady state. LDL-apolipoprotein B and LDL-cholesterol were measured directly after ultracentrifugation, and LDL-cholesterol also was estimated by the method of Friedewald. Steady-state atorvastatin pharmacokinetic parameters were estimated on the last day of each dosing period. LDL-cholesterol (Friedewald) reductions of 34%, 43%, and 57% were produced by atorvastatin doses of 5, 20, and 80 mg, respectively. The mean dose-response relationship was log linear, and almost all individual dose-response curves paralleled the mean curve. LDL-apolipoprotein B reductions were slightly less than those of LDL-cholesterol. Atorvastatin area under the curve (AUC (0-24) ) values increased proportionally with dose, while values of C max (maximum concentration) increased more than proportionally, and C min (minimum concentration) increased less than proportionally. Following initiation of dosing, statistically significant decreases in total cholesterol, LDL-cholesterol (beta quant), and LDL-apolipoprotein B were observed within 24 hours and in LDL-C (Friedewald) within 72 hours. Following discontinuation of drug dosing, statistically significant increases were observed in total cholesterol and LDL-cholesterol (Friedewald) within 48 hours and in LDL-cholesterol (beta quant) and LDL-apolipoprotein B within 72 hours. At each dose, an individual's LDL-cholesterol response was not correlated with AUC (0-24) . In conclusion, atorvastatin produces marked LDL-cholesterol reductions, the mean dose-response relationship is log linear, almost all individual dose-response curves parallel the mean dose-response curve, onset and cessation of action are rapid, the estimated and measured LDL-cholesterol are the same, LDL-cholesterol and LDL-Apo B reductions are similar, and plasma concentrations are not correlated with LDL-cholesterol reduction at a given dose.