Macrocyclic lactones: distribution in plasma lipoproteins of several animal species including humans.

We studied the in vitro distribution of macrocyclic lactones (MLs), lipophilic anthelmintic drugs, in the plasma of several animal species including humans. First, in vitro spiking of goat plasma was performed with ivermectin, moxidectin, abamectin, doramectin, or eprinomectin. In parallel, goats were treated with subcutaneous injection of ivermectin. Then, cow, sheep, rabbit, pig, and human plasma were spiked with moxidectin. Four fractions were separated using KBr density gradient ultracentrifugation: very-low-density lipoprotein (VLDL), low-density lipoprotein (LDL), high-density lipoprotein (HDL), and lipoprotein-deficient fraction. Cholesterol was analyzed by enzymatic assay and MLs by high-performance liquid chromatography. An average of 96% of MLs was associated with lipoproteins. The five MLs studied distributed similarly into goat plasma fractions with a preferential association with HDL (80-90%). Ivermectin partitioning in goat plasma was similar after in vitro spiking and in vivo treatment. In species displaying various lipoprotein profiles, moxidectin was also mainly associated with HDL. However, in human plasma, moxidectin was associated with a lesser extent to HDL (70%) and more to LDL (22%) when compared to other animal species. A relation between the plasma cholesterol content and pharmacokinetics of the drug is suggested. Our finding will allow further exploration of intestinal lymphatic absorption and milk elimination of these compounds-mechanisms in which lipoproteins are involved. In addition, possible improvements of new drug delivery systems are suggested.