Absorption, distribution, metabolism and excretion of peginesatide, a novel erythropoiesis-stimulating agent, in rats.

The pharmacokinetics (PK) (absorption, distribution, metabolism, excretion) of peginesatide, a synthetic, PEGylated, investigational, peptide-based erythropoiesis-stimulating agent (ESA), was evaluated in rats. The PK profile was evaluated at 0.1-5 mg·kg(-1) IV using unlabeled or [(14)C]-labeled peginesatide. Mass balance, tissue distribution and metabolism were evaluated following IV administration of 5 mg·kg(-1) [(14)C]-peginesatide, with tissue distribution also evaluated by quantitative whole-body autoradiography (QWBA) following an IV dose of 17 mg·kg(-1) [(14)C]-peginesatide. Plasma clearance was slow and elimination was biphasic with unchanged peginesatide representing >90% of the total radioactivity of the total radioactive exposure. Slow uptake of the radiolabeled compound from the vascular compartment into the tissues was observed. Biodistribution to bone marrow and extramedullary hematopoietic sites, and to highly vascularized lymphatic and excretory tissues occurred. A predominant degradation event to occur in vivo was the loss of one PEG chain from the branched PEG moiety to generate mono-PEG. Renal excretion was the primary mechanism (41%) of elimination, with parent molecule (67%) the major moiety excreted. In conclusion, elimination of [(14)C]-peginesatide-derived radioactivity was extended, retention preferentially occurred at sites of erythropoiesis (bone marrow), and urinary excretion was the primary elimination route.

The distribution, metabolism, and elimination of clofarabine in rats.

The distribution, metabolism, and elimination of intravenous [14C]clofarabine was studied in Fischer 344 male rats under a once daily for 5 days dosing schedule of 25 or 50 mg/kg/day. Also, the in vitro metabolism in rat, dog, and human hepatocytes was studied. Plasma radioactivity (of which clofarabine accounted for 63% to 93%) exhibited three phases of exponential elimination, with half-lives of 0.3, 1.3, and 12.8 h after administration of the 25 mg/kg/day regimen. Unscheduled deaths occurred after one to three doses with the 50 mg/kg regimen, possibly due to nonlinear pharmacokinetics; therefore, mass balance and radiokinetic profiles could not be obtained. A total of 77.1% (of which 87.2% was clofarabine) and 10.8% (of which 6.9% was clofarabine) of the dose was recovered in urine and feces, respectively. 6-ketoclofarabine, believed to be formed via adenosine deaminase, was the metabolite of greatest concentration found in urine and feces, but in each matrix, it accounted for only 7% of the daily recovery of radioactivity. 6-ketoclofarabine was also found in myocardium and liver but accounted for less than 2% of the total radioactivity in those tissues. Clofarabine was the major analyte found in myocardium (>97% region of integration) and liver (>94% region of integration). Whole body autoradiography demonstrated that the highest postdistributive concentrations of radioactivity were in the excretory organs, kidney, bladder, and gastrointestinal tract, with no remarkable suborgan distribution. In rat, dog, and human hepatocytes, 95, 96, and 99.8% [14C]clofarabine remained, respectively, after 6 h of incubation. Eleven metabolites were observed, with the largest constituting 2.5% of the radioactivity.