Xa Chromogenic Assay Research Articles

Laboratory monitoring of rivaroxaban and assessment of its bleeding risk

Background: The aims of this study were to investigate the effects of rivaroxaban on routine coagulation assays using our local, widely available, reagents and to study the relationship between sensitive coagulation assays and bleeding risk caused by rivaroxaban.Methods: Prothrombin time (PT), activated partial thromboplastin time (APTT) and anti-factor Xa (FXa) chromogenic assays (Biophen DiXaI) and inhibition of FXa activity were performed in normal pooled plasma (NPP) spiked with rivaroxaban and plasma samples from patients treated with rivaroxaban.Results: In vitro, the linear correlation coefficient of measured concentrations of rivaroxaban, by Biophen DiXaI, and spiked concentrations of rivaroxaban was 0.99. PT and APTT showed good linear correlation with rivaroxaban concentrations, while other assays showed poor correlation. In vivo, PT showed a moderate linear correlation with rivaroxaban concentrations while APTT had a weak correlation with rivaroxaban concentrations. In vitro and in vivo, the rivaroxaban concentrations, measured by Biophen DiXaI, always showed good correlation with the inhibition of FXa activity, and PT values showed moderate correlation with the inhibition of FXa activity.Conclusions: Biophen DiXaI can be considered as a quantitative method to monitor the anticoagulation activity of rivaroxaban, and could be used to evaluate bleeding risk caused by rivaroxaban. The PT reagent (Thrombosis S) could be considered as a rough method to monitor the anticoagulation activity of rivaroxaban and evaluate bleeding risk caused by rivaroxaban.

Comparison of Low-Molecular-Weight Heparins Prepared From Bovine Lung Heparin and Porcine Intestine Heparin

Currently porcine intestine is the only approved source for producing pharmaceutical heparin in most countries. Enoxaparin, prepared by benzylation and alkaline depolymerization from porcine intestine heparin, is prevalent in the anticoagulant drug market. It is predicted that porcine intestine heparin–derived enoxaparin (PIE) will encounter shortage, and expanding its production from heparins obtained from other animal tissues may, therefore, be inevitable. Bovine lung heparin is a potential alternative source for producing enoxaparin. Critical processing parameters for producing bovine lung heparin–derived enoxaparin (BLE) are discussed. Three batches of BLEs were prepared and their detailed structures were compared with PIEs using modern analytical techniques, including disaccharide composition, intact chain mapping by liquid chromatography-mass spectrometry and 2-dimensional nuclear magnetic resonance spectroscopy. The results suggested that the differences between PIEs and BLEs mainly result from N-acetylation differences derived from the parent heparins. In addition, bioactivities of BLEs were about 70% of PIEs based on anti-factor IIa and Xa chromogenic assays. We conclude that BLE has the potential to be developed as an analogue of PIE, although some challenges still remain.

Monitoring of heparins in haemodialysis using an anti-factor-Xa-specific whole-blood clotting assay

In haemodialysis low-molecular-weight (LMW) heparin is increasingly used for anticoagulation. The advantages over unfractionated (UF) heparin are the lower bleeding risk and the lack of influence on lipid metabolism. However, no reliable and rapid method is available so far to control the efficacy and safety of LMW heparin during haemodialysis. The specific anti-factor Xa (aXa) chromogenic substrate assays are laborious and time consuming. In the present study we have compared chromogenic assay with a coagulation assay (heptest), which was performed from plasma and whole-blood samples. The effects were compared with unfractionated heparin during haemodialysis. The aXa activity in the chromogenic S2222 assay ranged between 0.2 and 0.5 U/ml with UF heparin and between 0.4 and 0.8 U/ml with LMW heparin during haemodialysis. The coagulometric aXa activity in heptest assay from plasma was 0.6-1.0 U/ml with UF heparin and 1.2-2.0 U/ml with LMW heparin. The Heptest coagulation values from citrated whole blood samples ranged from 0.4 to 0.8 U/ml with UF heparin and from 0.8 to 1.4 U/ml with LMW heparin. The prolongation of the heptest clotting times with UF and LMW heparin was in the range of 4.4 for UF heparin and 5.2 for LMW heparin using the whole-blood assay. Heptest assay from plasma samples yielded prolongations of 6.1 with UF heparin and 6.6 with LMW heparin. The data show that the coagulation assay is rapid and reproducible using plasma or uncentrifuged whole-blood samples and is valid to monitor UF heparin or LMW heparin in patients undergoing chronic intermittent haemodialysis.