Direct oral anticoagulants (DOACs), the thrombin inhibitor dabigatran and the anti-Xa inhibitors rivaroxaban and apixaban are currently licensed for thromboprophylaxis after orthopaedic surgery, in non-valvular atrial fibrillation, and treatment of deep vein thrombosis and uncomplicated pulmonary embolism. The drugs are easy to use, as standard dosing is recommended and no routine monitoring of coagulation is advocated. However, in cases of acute thrombosis or bleeding, emergency surgery, renal or hepatic failure, overdose and suspected non-adherence, assessing anticoagulant bioactivity is essential for safe and effective treatment. The aims of this study were to firstly assess the effects of these DOACs in commonly used coagulation screening tests (PT, INR and APTT) using both spiked samples and samples collected from patients on treatment. Secondly, the availability of specific methods for drug effect assessment, namely drug-calibrated thrombin time (dabigatran) and anti-Xa (rivaroxaban, apixaban) assays were assessed in surveys with European laboratories (n=86). Thirdly, the effects of DOACs on these specific assays were explored using patient samples. Finally, the effect of DOACs on the global coagulation assay thrombin generation (TG) was assessed in patients using dabigatran, rivaroxaban or apixaban. The spiked sample laboratory survey included 73 laboratories for dabigatran, 22 laboratories for rivaroxaban and 21 laboratories for apixaban. The laboratories performed coagulation assays in samples spiked with varying concentrations of the drug. A variety of different analysers and reagents were observed, with 24 different coagulation analysers, 13 different PT reagents and 10 different APTT reagents used in the investigated laboratories. The effects of all DOACs on INR were modest, but large reagent variability was noted in the responses, with the Quick-type reagents being more sensitive to the effects of dabigatran (p<0.001). In APTT, rivaroxaban and apixaban prolonged the APTT only modestly, but with dabigatran there was a clear prolongation, albeit the variability between laboratories was large (CVs 13-19% for all DOACs). Only about a fourth of these (in the surveys ranging from 15-36% of the participants) were able to provide more specific methods, TT or anti-Xa assays for drug quantification at that time. Dabigatran effects in patient samples were different than what was observed in the surveys using spiked samples. We studied dabigatran effects in 241 unselected patient samples. The effect on PT was very modest, with little prolongation. In APTT, there was a curvilinear relationship (R2 = 0.71) with dabigatran. However, the sensitivity effects among patients varied, with some patients having a normal APTT at dabigatran levels up to 160 ng/mL. In the specific assays, diluted thrombin time, ecarin clotting assay and anti-IIa assay accurately quantified dabigatran concentrations as confirmed by mass spectrometry (R2 = 0.81, 0.96 and 0.90, respectively). In the RVVT and PiCT assays, the correlations with diluted thrombin time were modest (R2 = 0.49 and 0.73, respectively). In TG, a paradoxical increase was observed in the endogenous thrombin potential (ETP) and Peak TG, while lag time also prolonged with increasing concentrations of dabigatran. Rivaroxaban and apixaban effects on coagulation in patient samples were further assessed in a well-characterised group of patients using these drugs for thromboprophylaxis after orthopaedic surgery. In this study, a noticeable inflammatory response after the surgery was evident, with a mean C reactive protein (CRP) of over 100 mg/L at one week after surgery, while haemoglobin and albumin were clearly below the reference intervals. This inflammatory setting was also reflected by the increases in FVIII:C and fibrinogen at one week after surgery. We observed clear differences between responses to rivaroxaban and apixaban. Rivaroxaban peak levels were higher and trough levels lower than with apixaban. This reflects the fact that rivaroxaban is dosed only once daily (10 mg once daily), while apixaban twice daily (2.5 mg twice daily), with corresponding steady state peak levels of 184 ng/mL and 135 ng/mL, respectively. It is noteworthy that the difference between these drugs extended to responses in TG; the ETP response at peak drug levels was strong with rivaroxaban, whereas with the trough drug levels, the TG parameters were close to the baseline levels. With apixaban the responses were more stable. The RVVT, used as a qualitative test, detected prolongation only at rivaroxaban peak levels. In conclusion, from the surveys performed we encountered large diversity in different reagents used and assays offered among European laboratories, with a wide variability in results. In the studies with patient samples, it became evident that many factors other than drug concentration influence the responses in coagulation assays and TG, which reflects the coagulation status of the patients. In clinical practice, care and diligence is required when assessing and interpreting the effects of DOACs on patients.
|Myöntöpäivämäärä||25 elok. 2017|
|Tila||Julkaistu - 2017|
|OKM-julkaisutyyppi||G5 Tohtorinväitöskirja (artikkeli)|
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