Mass balance and biotransformation of finerenone, a nonsteroidal mineralocorticoid receptor antagonist, were investigated in four healthy male volunteers following a single oral administration of 10 mg (78 μCi) of [14C]finerenone and compared with data from studies in dogs and rats. The total recovery of the administered radioactivity was 101% in humans, 94.7% in dogs, and 95.2% in rats. In humans, radioactivity was mainly excreted renally (80%); in rats, it was primarily the biliary/fecal route (76%); and in dogs, excretion was more balanced. Finerenone was extensively metabolized in all species by oxidative biotransformation, with minor amounts of unchanged drug in excreta (humans: 1%; dogs, rats: <9%). In vitro studies suggested cytochrome P450 3A4 was the predominant enzyme involved in finerenone metabolism in humans. Primary metabolic transformation involved aromatization of the dihydronaphthyridine moiety of metabolite M1 as a major clearance pathway with a second oxidative pathway leading to M4. These were both prone to further oxidative biotransformation reactions. Naphthyridine metabolites (M1–M3) were the dominant metabolites identified in human plasma, with no on-target pharmacological activity. In dog plasma, finerenone and metabolite M2 constituted the major components; finerenone accounted almost exclusively for drug-related material in rat plasma. For metabolites M1–M3, axial chirality was observed, represented by two atropisomers (e.g., M1a and M1b). Analysis of plasma and excreta showed one atropisomer (a-series, >79%) of each metabolite predominated in all three species. In summary, the present study demonstrates that finerenone is cleared by oxidative biotransformation, mainly via naphthyridine derivatives.
Summary Rivaroxaban is an oral, direct factor Xa inhibitor. Routine coagulation monitoring is not required, but a quantitative determination of rivaroxaban concentrations might be useful in some clinical circumstances. This multicentre study assessed the suitability of the anti-factor Xa chromogenic assay for the measurement of rivaroxaban plasma concentrations (ng/ml) using rivaroxaban calibrators and controls, and the inter-laboratory precision of the measurement. Twenty-four centres in Europe and North America were provided with sets of rivaroxaban calibrators (0, 41, 209 and 422 ng/ml) and a set of rivaroxaban pooled human plasma controls (20, 199 and 662 ng/ml; the concentrations were unknown to the participating laboratories). The evaluation was carried out over 10 days by each laboratory using local anti-factor Xa reagents as well as the centrally provided reagent, a modified STA® Rotachrom® assay. A calibration curve was produced each day, and the day-to-day precision was evaluated by testing three human plasma controls. When using the local anti-factor Xa reagents, the mean rivaroxaban concentrations (measured/actual values) were: 17/20, 205/199 and 668/662 ng/ml, and the coefficient of variance (CV) was 37.0%, 13.7% and 14.1%, respectively. When the modified STA Rotachrom method was used, the measured/actual values were: 18/20, 199/199 and 656/662 ng/ml, and the CV was 19.1%, 10.9% and 10.0%, respectively. The results suggest that, by using rivaroxaban calibrators and controls, the anti-factor Xa chromogenic method is suitable for measuring a wide range of rivaroxaban plasma concentrations (20–660 ng/ml), which covers the expected rivaroxaban plasma levels after therapeutic doses.
Summary Rivaroxaban is a direct factor Xa inhibitor, which can be monitored by anti-factor Xa chromogenic assays. This ex vivo study evaluated different assays for accurate determination of rivaroxaban levels. Eighty plasma samples from patients receiving rivaroxaban (Xarelto®) 10 mg once daily and 20 plasma samples from healthy volunteers were investigated using one anti-factor Xa assay with the addition of exogenous antithrombin and two assays without the addition of antithrombin. Two different lyophilised rivaroxaban calibration sets were used for each assay (low concentration set: 0, 14.5, 59.6 and 97.1 ng/ml; high concentration set: 0, 48.3, 101.3, 194.2 and 433.3 ng/ml). Using a blinded study design, the rivaroxaban concentrations determined by the assays were compared with concentrations measured by HPLC-MS/MS. All assays showed a linear relationship between the rivaroxaban concentrations measured by HPLC-MS/MS and the optical density of the anti-FXa assays. However, the assay with the addition of exogenous anti-thrombin detected falsely high concentrations of rivaroxaban even in plasma samples from controls who had not taken rivaroxaban (intercept values using the high calibrator set and the low calibrator set: +26.49 ng/ml and +13.71 ng/ml, respectively). Plasma samples, initially determined by the high calibrator setting and containing rivaroxaban concentrations <25 ng/ml, had to be re-run using the low calibrator setting for precise measurement. In conclusion, anti-factor Xa chromogenic assays that use rivaroxaban calibrators at different concentration levels can be used to measure accurately a wide range of rivaroxaban concentrations ex vivo. Assays including exogenous antithrombin are unsuitable for measurement of rivaroxaban.
Research into new anticoagulants for preventing and treating thromboembolic disorders has focused on targeting single enzymes in the coagulation cascade, particularly Factor Xa and thrombin, inhibition of which greatly decreases thrombin generation. Based on the results of phase III clinical trials, rivaroxaban, a direct Factor Xa inhibitor, has been approved in many countries for the management of several thromboembolic disorders. Owing to its predictable pharmacokinetic and pharmacodynamic characteristics, fixed-dose regimens are used without the need for routine coagulation monitoring. In situations where assessment of rivaroxaban exposure may be helpful, anti-Factor Xa chromogenic assays (in tandem with standard calibration curves generated with the use of rivaroxaban calibrators and controls) could be used. It is important to note that test results will be affected by the timing of blood sampling after rivaroxaban intake. In addition, the anti-Factor Xa method measures the drug concentration and not the intensity of the drug’s anticoagulant activity, and a higher than expected rivaroxaban plasma level does not necessarily indicate an increased risk of bleeding complications. Therefore, clinicians need to consider test results in relation to the pharmacokinetics of rivaroxaban and other patient risk factors associated with bleeding.
