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 Cmax (maximum concentration) increased more than proportionally, and Cmin (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.