Relationship between plasma fenofibric acid levels and the effect of micronized fenofibrate on cholesterol, low-density-lipoprotein cholesterol and apolipoprotein B in patients with primary hypercholesterolemia

Objective: We examined the relationship between plasma levels of fenofibric acid, the active metabolite of fenofibrate, and differences in concentrations of plasma lipids, in subjects with primary type IIA or IIB hyperlipoproteinemia (HLP). Subjects and methods: Twenty-nine patients (13 with type IIA and 16 with type IIB HLP) were treated with a single daily 200-mg dose of micronized fenofibrate for 3 months, after which the plasma levels of fenofibric acid were determined by HPLC after an overnight fast. Results: In the type IIA HLP phenotype, statistically significant correlations were found between fenofibric acid levels and changes in total cholesterol, LDL-C and apo-B at all three control visits, with the highest correlation coefficients at V3 visit (total cholesterol r = 0.85, LDL-C r = 0.68, apo-B r = 0.85). In type IIB HLP, statistical significance was confirmed only when performing an analysis of pooled values for total cholesterol and LDL-C (r = 0.42, r = 0.34, respectively). The high correlation between plasma fenofibric acid levels and its effect on betalipoprotein changes might reflect the effect of fenofibrate on the catabolism of plasma LDL by the LDL receptor, since that type of relationship is typical of drugs which directly influence the target compartment without an effect on intermediary steps of metabolism. An explanation for the different levels of correlations in type IIA and IIB patients might be found in their different metabolic defects. The fact that fenofibrate's impact on VLDLs is such an important part of its effect on lipoprotein metabolism supports the concept that the effect of circulating fenofibric acid is less pronounced on the LDL receptor in type IIB HLP.