RESUMEN
INTRODUCTION: Apixaban is an oral direct factor Xa inhibitor developed for the prophylaxis and treatment of thromboembolic disorders. Laboratory monitoring is not necessary, but the effects on common coagulation reagents and assays constitute clinically valuable information. OBJECTIVES: To investigate the effects of apixaban on commonly used coagulation methods, and to evaluate anti-FXa assays for specific determination of the drug concentration. MATERIALS AND METHODS: Apixaban was added to plasma from healthy subjects in the concentration range 0-1000 µg L(-1) , and analyses were performed with different reagents for activated partial thromboplastin time (APTT), prothrombin time (PT), antithrombin, protein C, and protein S. A lupus anticoagulant assay and an APTT assay with varying phospholipid concentrations were used to study the phospholipid dependence. RESULTS: In general, apixaban showed fewer effects in vitro than have been shown for rivaroxaban, another direct FXa inhibitor. The concentration needed to double the APTT varied between 2200 and 4700 µg L(-1) , and the concentration needed to double the PT varied between 700 and 3900 µg L(-1) . The effects on antithrombin, protein C and protein S assays were dependent on the type of reagent. Apixaban did not cause false-positive lupus anticoagulant results. Chromogenic anti-FXa assays showed linear dose-response curves with apixaban. CONCLUSIONS: Therapeutic concentrations of apixaban variably affect different assay groups, and even different reagents within an assay group. The effects were much smaller than with rivaroxaban. The use of APTT and/or PT assays to screen the anticoagulant activity of apixaban cannot be recommended. A chromogenic anti-FXa assay can be used for reliable measurements of apixaban concentration.
Asunto(s)
Coagulación Sanguínea/efectos de los fármacos , Inhibidores del Factor Xa/química , Factor Xa/química , Pirazoles/química , Piridonas/química , Administración Oral , Calibración , Reacciones Falso Positivas , Voluntarios Sanos , Humanos , Relación Normalizada Internacional , Inhibidor de Coagulación del Lupus/química , Morfolinas/química , Tiempo de Tromboplastina Parcial , Fosfolípidos/química , Proteína C/química , Proteína S/química , Tiempo de Protrombina , Reproducibilidad de los Resultados , Rivaroxabán , Tiofenos/químicaRESUMEN
STUDY QUESTION: Do thrombin generation and haemostatic parameters differ during the two phases of the menstrual cycle? SUMMARY ANSWER: Total thrombin concentration is higher during the luteal phase compared with the follicular phase of the menstrual cycle. WHAT IS KNOWN ALREADY: The coagulation cascade is affected by many variables, such as fluctuations in the levels of sex hormones. The studies on the variations in haemostatic parameters during the menstrual cycle have produced diverse results. STUDY DESIGN, SIZE, DURATION: Thrombin generation and selected haemostatic parameters (fibrinogen, factor II, factor VII, factor VIII, factor X, von Willebrand factor, antithrombin and D-dimer) were measured during the two phases of a normal menstrual cycle in 102 healthy women not taking any form of hormone medication. PARTICIPANTS/MATERIALS, SETTING, METHODS: The study cohort consisted of 102 healthy women with regular menstrual cycles. Thrombin generation was measured by the calibrated automated thrombogram method. Progesterone and sex hormone-binding globulin were measured by chemiluminescence enzyme immunoassays. Estradiol was measured by a sensitive radioimmunoassay. Fibrinogen was measured by a clotting method, antithrombin was measured by a chromogenic method and factor II, factor VII, factor VIII, factor X, von Willebrand factor and D-dimer were measured by photometric methods. MAIN RESULTS AND THE ROLE OF CHANCE: It was shown that the total amount of generated thrombin (Endogenous Thrombin Potential) was significantly higher during the luteal compared with the follicular phase (P = 0.027). Factor X was significantly higher during the follicular phase (P = 0.028). Progesterone exhibited significant associations (measured by the least squares regression analysis) with fibrinogen and factor X during the follicular phase (P = 0.043 and P = 0.033, respectively) and with factors II and VII during the luteal phase (P = 0.034 and P = 0.024, respectively). The validity of the results from the regression analysis was further confirmed by performing correlation analyses (Pearson correlation matrix) for haemostatic markers for the luteal and follicular phases (accepted correlation level >0.8). LIMITATIONS, REASONS FOR CAUTION: The wide confidence interval for the differences in endogenous thrombin potential during the two phases could imply that the size of the cohort may not be sufficient to fully evaluate the biological variations. Additionally, the haemostatic markers were not shown to have significant associations with thrombin generation, suggesting that the increased thrombin concentration during the luteal phase would be mediated by another mechanism, as yet unidentified. WIDER IMPLICATIONS OF THE FINDINGS: The associations between progesterone and the haemostatic markers, as shown for both phases of the menstrual cycle, suggest a previously unknown or undefined yet potentially significant role for progesterone in the coagulation system. However, it has been shown that the use of progestogen-only preparations does not affect the coagulation system, which is partly the reason why they are considered safe for women with thrombophilia or previous thrombotic event. Further studies are required in order to demonstrate whether our results can be extrapolated for synthetic progestins, which might have significant implication on the indications for their use.
Asunto(s)
Fase Folicular/metabolismo , Fase Luteínica/metabolismo , Trombina/metabolismo , Adulto , Coagulación Sanguínea/fisiología , Femenino , Fibrinógeno/metabolismo , Humanos , Progesterona/metabolismo , Análisis de Regresión , Globulina de Unión a Hormona Sexual/metabolismoRESUMEN
INTRODUCTION: Rivaroxaban is an oral direct factor Xa inhibitor developed for prophylaxis and treatment of thromboembolic disorders. Laboratory monitoring is not necessary but the dose-dependent effects on common reagents and assay procedures are largely unknown. OBJECTIVES: To investigate the effect of rivaroxaban on commonly used coagulation assays. MATERIALS AND METHODS: Rivaroxaban was added to plasma from healthy subjects in the concentration range 0-1000 µg L(-1) and analyzed using different reagents for activated partial thromboplastin time (APTT), prothrombin time (PT), antithrombin, fibrinogen and activated protein C (APC) resistance assays. RESULTS: At an expected peak concentration of rivaroxaban in clinical use, the APTTs were almost invariably prolonged but at lower concentrations the effect was weak. The concentration needed to double the APTT varied between 389 ± 106 and 617 ± 149 µg L(-1) for different reagents. The PT assays showed a marked degree of difference. In general, the Quick PT type assays were more sensitive compared with the Owren type PT assays. The results from antithrombin assays were dependent on the type of reagent, with the Xa-based assay being sensitive for rivaroxaban with an estimated increase of 0.09 IU mL(-1) per 100 µg L(-1) rivaroxaban. There were only minor effects on fibrinogen assays based on thrombin reagents. The APTT-based assay for APC resistance is affected in a dose-dependent manner whereas an assay based on the activation of coagulation at the prothrombinase level was unaffected. CONCLUSIONS: Different assays, and even different reagents within an assay group, display variable effects by therapeutic concentrations of rivaroxaban.
Asunto(s)
Anticoagulantes/administración & dosificación , Pruebas de Coagulación Sanguínea , Coagulación Sanguínea/efectos de los fármacos , Inhibidores del Factor Xa , Morfolinas/administración & dosificación , Tiofenos/administración & dosificación , Resistencia a la Proteína C Activada/sangre , Administración Oral , Adulto , Antitrombinas/metabolismo , Relación Dosis-Respuesta a Droga , Femenino , Fibrinógeno/metabolismo , Humanos , Masculino , Tiempo de Tromboplastina Parcial , Valor Predictivo de las Pruebas , Tiempo de Protrombina , Reproducibilidad de los Resultados , RivaroxabánRESUMEN
This study investigated whether the addition of endothelial cells to blood or blood plasma is of value in global laboratory diagnostic testing for thrombotic tendency. Plasma from thrombotic patients and healthy individuals was exposed to human umbilical vein endothelial cells (HUVEC), in monolayers or suspensions, and fibrin deposition or clotting time, respectively, was registered. The latter was determined by a novel rheometric procedure that also gave information about coagulum rigidity. Plasma from patients (n = 10) tended to deposit more fibrin on HUVEC monolayers than plasma from healthy individuals (n = 10). When mixed with suspended HUVEC, plasma from patients (n = 14) showed shorter clotting times than plasma from healthy individuals [n = 13; 4.79 +/- 1.02 min (mean +/- SD) compared with 6.80 +/- 1.50 min, P < 0.001]. Coagulum rigidity among patients also differed from that of healthy individuals (P < 0.05). The study showed that the addition of endothelial cells to blood plasma is of value in global laboratory diagnostic testing for thrombotic tendency.