DISCUSSION
duodenal bile, duodenal bile sampling, CKD, anemia
ANEMIA
Following a single oral dose of [Consistently, previous steady‐state clinical data in patients with anemia associated with various stages of CKD also indicated that daprodustat was the principal circulating DRM in human plasma, measured at up to 55% by AUC ratio.Comprehensive safety evaluations of the three major metabolites have therefore been conducted, and adequate toxicology and safety qualifications established throughout the development program.Notably, the presence of unchanged daprodustat in human feces and urine was low (approximately 0.5% of dose), whereas oxidative metabolites, essentially the same as those in plasma, accounted for the vast majority of radioactivity. In addition, the radio‐metabolic profile in human duodenal bile following a microtracer IV infusion of [Proposed scheme of metabolites of [Five of the six predominant circulating human metabolites (M3, M4, M5, M6, and M13) contain chiral centers and could therefore exist in multiple stereoisomeric forms (M2 does not contain a chiral center). In a previous analysis of human urine samples (data not shown), metabolites M2, M3, M4, and M13 were determined to be present as single stereoisomers (i.e., GSK2391220 [M2, achiral], GSK2506104 [M3], GSK2487818 [M4], and GSK2531401 [M13]). Metabolites M5 and M6 were detected as pairs of stereoisomers consisting of GSK2506102 (79%) and GSK2531399 (21%) for M5, and GSK2531398 (89%) and GSK2531407 (11%) for M6. Further chiral analysis of metabolites M3 and M13 in plasma samples (data not shown) confirmed that the predominant circulating human stereoisomers of M3 and M13 were GSK2536104 and GSK2531401, respectively. The defined predominant stereoisomeric form for each metabolite (i.e., GSK2391220 for M2 [achiral], GSK2506104 for M3, GSK2487818 for M4, GSK2506102 for M5, GSK2531398 for M6, and GSK2531401 for M13) has been used in the safety evaluations and method development and validation of achiral bioanalytical assays.In human hepatocytes, [It is worth mentioning that quantitation of more than a dozen circulating DRMs can be challenging due to limitations of instrument sensitivity. In the current study, the quantitative measurement of plasma radioactive peaks on a conventional TopCount microplate counter was enabled through robust multiple HPLC injection/cumulative fraction collection. With a single injection, the LLQ would have been 6% of the total sample radioactivity for the 0–8 h plasma pool, and the majority of the quantified peaks reported in the current study would have been undetected or at least below the LLQ. Since the analytical sensitivity is in proportion to the number of injections, this multiple HPLC injection approach has lowered the LLQ to 1%, and greatly improved the accuracy of daprodustat metabolite profiling. Along with the deconvolution method for the determination of the individual level of M2, it ensured confirmation that all predominant metabolites were less than the threshold of 10% of total DRM in human plasma after a single dose to healthy subjects.The inclusion of duodenal bile sampling in human ADME studies is still a relatively rare activity as, historically, bile collection was done using an invasive approach.In summary, following oral dosing of radiolabeled daprodustat, a large proportion of the dose was absorbed, primarily cleared by oxidative metabolism and eliminated via hepatobiliary and urinary excretion. Unchanged daprodustat was the principal circulating DRM with each of the six predominant metabolites individually representing <10% of DRM.