The objective of this study was to validate the analytical method for the determination of a parent compound and its main metabolites (M1 and M2) in human plasma, over a concentration range of 0.1 to 20 pg/mL (parent) and 0.25 to 20 pg/mL (M1 and M2).  A sample aliquot volume of 500 µL was used.  This assay concentration range was required due to the high potency and hence low therapeutic doses of the parent compound administered.  The typical C_max was expected to be in the low pg/mL levels.