In vitro metabolism of rivaroxaban, an oral, direct factor Xa inhibitor, in liver microsomes and hepatocytes of rats, dogs, and humans.

The in vitro metabolism of rivaroxaban, a novel, oral, direct factor Xa inhibitor for the prevention and treatment of thromboembolic disorders, was investigated in several species, including humans. The objective of this study was to elucidate metabolite structures and identify the metabolic pathways to provide support for in vivo safety and clinical studies. [(14)C]Rivaroxaban was incubated with liver microsomes and hepatocytes of rats, dogs, and humans. The samples were analyzed by high-performance liquid chromatography-(14)C-tandem mass spectroscopy, to generate metabolite profiles and propose or confirm the structures of the metabolites formed. In vitro metabolite profiles showed no major differences between species. The main oxidative metabolic pathways identified for all species were hydroxylation at the morpholinone moiety (M-2, M-3, and M-8) and to a lesser extent at the oxazolidinone moiety (M-9). M-2 was the main metabolite in all microsomal incubations. M-1, a morpholinone ring-opened product formed by further oxidation of M-2, was the main metabolite in all hepatocyte incubations. Other pathways were amide hydrolysis at the morpholinone ring (M-7) and the chlorothiophene amide moiety (M-13 and M-15). In hepatocytes, M-13 was readily conjugated with glycine, leading to M-4. The metabolic fate of unlabeled M-15 was investigated separately. Incubations with human liver microsomes and hepatocytes showed that M-15 was first oxidized to the aldehyde intermediate M-16 and subsequently reduced to M-17 (alcohol) or oxidized to M-18 (carboxylic acid). No metabolism at the chlorothiophene moiety itself was found. Overall, rivaroxaban showed no species differences in metabolism, with different independent metabolic pathways and no formation of reactive metabolites.

Metabolism and excretion of rivaroxaban, an oral, direct factor Xa inhibitor, in rats, dogs, and humans.

Rivaroxaban is a novel, oral, direct factor Xa inhibitor for the prevention and treatment of thromboembolic disorders. The objective of this study was to investigate the in vivo metabolism and excretion of rivaroxaban in rats, dogs, and humans. Single doses of [(14)C]rivaroxaban (3 and 1 mg/kg) were administered to rats (orally/intravenously) and dogs (orally), respectively. A single oral dose of [(14)C]rivaroxaban (10 mg) was administered to healthy human males (n = 4). Plasma and excreta were collected and profiled for radioactivity. Recovery of total radioactivity was high and > or = 92% in all species. Unchanged rivaroxaban was the major compound in plasma at all time points investigated, across all species. No major or pharmacologically active circulating metabolites were detected. Rivaroxaban and its metabolites were rapidly excreted; urinary excretion of radioactivity was 25 and 52%, and fecal excretion was 67 and 43% of the dose in rats and dogs, respectively. In humans, 66% of the dose was excreted renally (36% unchanged drug) and 28% in the feces. Radioactivity profiles in excreta were similar across species. Three metabolic pathways were identified: oxidative degradation of the morpholinone moiety (major pathway) and hydrolysis of the central amide bond and of the lactam amide bond in the morpholinone ring (minor pathways). M-1, the main metabolite in excreta of all species, was eliminated via both renal and fecal/biliary routes. In total, 82 to 89% of the dose administered was assigned to unchanged rivaroxaban and its metabolites in the excreta of rats, dogs, and humans.

Tracheobronchial amyloidosis--bronchoscopic diagnosis and therapy of an uncommon disease: a case report.

We report on a 65-year-old female who complained of recurrent bronchopulmonary infections since 1999. She suffered from permanent cough and progressive dyspnea. The diagnosis of amyloidosis was made by bronchoscopic tissue biopsies, during which severe bleeding occurred. Argon-plasma-laser treatment stopped the bleeding and resulted in a successful recanalization of the left main bronchus. The patient noticed a decrease in dyspnea shortly after the intervention. Further diagnostic procedures did not show any signs of systemic or malignant disease. This led us to the diagnosis of a rare form of isolated tracheobronchial amyloidosis.

Pharmacokinetics of BAY 59-7939--an oral, direct Factor Xa inhibitor--in rats and dogs.

The pharmacokinetics of BAY 59-7939 - a novel, oral, direct Factor Xa inhibitor - were investigated in rats and dogs in support of preclinical safety studies and clinical development. BAY 59-7939 was rapidly absorbed after oral dosing, with an absolute bioavailability of 57-66% in rats, and 60-86% in dogs. Plasma pharmacokinetics of BAY 59-7939 were linear across the investigated dose range (1-10 mg kg(-1) in rats, 0.3-3 mg kg(-1) in dogs). Plasma clearance was low: 0.4 l kg(-1) h(-1) in rats and 0.3 l kg(-1) h(-1) in dogs; volume of distribution (V(ss)) was moderate: 0.3 l kg(-1) in rats, and 0.4 l kg(-1) in dogs. The elimination half-life after oral administration was short in both species (0.9-2.3 h). Whole-body autoradiography showed moderate tissue affinity. No retention or small volume enrichments of BAY 59-7939-related radioactivity were observed. The plasma-protein binding of BAY 59-7939 was high, species dependent and fully reversible. BAY 59-7939 was rapidly excreted in rats and dogs, and was not irreversibly retained. A dual mode of excretion (biliary/faecal and renal) was observed. In summary, BAY 59-7939 had a favourable, predictable pharmacokinetic profile, with high oral bioavailability and a dual route of excretion.

Investigation of the stereoselective in vitro biotransformation of glutethimide by high-performance liquid chromatography and capillary electrophoresis.

Due to our interest in drugs with a glutarimide structure, we reinvestigated the stereoselectivity of the in vitro biotransformation of the chiral hypnotic-sedative drug glutethimide. Glutethimide enantiomers were separated on a preparative scale by HPLC on cellulose tris(4-methylbenzoate) as chiral stationary phase. The enantiomeric purity was higher than 99%. A reversed-phase HPLC method was developed to determine the metabolites of glutethimide. After incubations with rat liver microsomes both enantiomers formed 5-hydroxyglutethimide as the main metabolite, as well as additional metabolites, of which some were formed stereoselectively. Mass spectrometry of the unknown metabolites indicated a hydroxylation in the ethyl side chain for two of the metabolites. A third metabolite was tentatively identified as desethylglutethimide.

Investigation of the in vitro biotransformation and simultaneous enantioselective separation of thalidomide and its neutral metabolites by capillary electrophoresis.

Reversed-phase liquid chromatography is a long established method for the analysis of drug metabolism. The current investigation demonstrates that micellar electrokinetic capillary chromatography can be an attractive alternative. Two methods were developed using sodium dodecyl sulfate and hexadecyltrimethylammonium bromide for the determination of possible hydroxylated metabolites of the former sedative drug thalidomide (Contergan) in order to study the in vitro metabolism of the drug by incubation with rat liver microsomes. The biotransformation was found to be stereoselective: S-(-)-thalidomide mainly formed 5-hydroxythalidomide, whereas R-(+)-thalidomide was preferentially transformed to two metabolites tentatively assigned to be diastereomers of 5'-hydroxythalidomide. Furthermore, the simultaneous enantioseparation of thalidomide and two of its possible hydroxylated metabolites was achieved using capillary electrophoresis with negatively charged carboxymethyl-beta-cyclodextrin. The dependencies of the selectivity of the enantioseparation on the concentration of the chiral additive and the pH of the run buffer were investigated.