Comparison of rivaroxaban concentrations between Asians and Caucasians and their correlation with PT/INR

Simvastatin, but Not Atorvastatin, Is Associated with Higher Peak Rivaroxaban Serum Levels and Bleeding: an Asian Cohort Study from Singapore

AIMS

This study attempts to identify predictors associated with bleeding and stroke and systemic embolism (SSE) in Singaporean Asians taking rivaroxaban and apixaban.

METHODS

A total of 134 Singaporean patients on either rivaroxaban or apixaban for non-valvular atrial fibrillation were included for this study. Baseline characteristics were recorded at recruitment while bleeding and SSE events were recorded during a 1-year follow-up. Peak and trough drug plasma concentrations were collected based on the dosing interval and pharmacokinetics of the drugs and quantified using high performance liquid chromatography. Characteristics of patients with or without bleeds were compared using relevant statistical tests. Multivariable regression that included covariates with p < 0.1 from an initial univariable regression was performed to analyse predictors that resulted in higher risk of bleeding in patients.

RESULTS

Median creatinine clearance (CrCl) was significantly lower in patients on rivaroxaban who experienced bleeds as compared to patients who did not experience bleeds (61.5 vs 70.8 mL/min, p = 0.047), while concomitant simvastatin use was found to be independently associated with a sixfold increased risk of bleeding (adjusted OR = 6.14 (95% CI: 1.18-31.97), p = 0.031) for rivaroxaban after controlling for body mass index, CrCl and having experienced a previous SSE.

CONCLUSION

Our findings suggest that concomitant use of simvastatin with rivaroxaban may be associated with bleeding events in an Asian cohort. Further studies using physiologically based pharmacokinetic modelling are required to investigate the drug-drug interactions between these drugs.

A Case of Symptomatic Supratherapeutic International Normalized Ratio on Rivaroxaban

Rivaroxaban is a direct oral anticoagulant that works by inhibiting factor Xa. Direct anticoagulants have largely replaced direct vitamin K inhibitors (VKAs) due to the decreased risk of major hemorrhages and the lack of need for regular monitoring and dose adjustments. However, there have been multiple reports of elevated international normalized ratio (INR) and bleeding incidents in patients on rivaroxaban, which brings into question the potential need for monitoring. We report a case of an INR of 4.8 in a rivaroxaban-naïve patient who presented with gastrointestinal bleeding and a significant drop in hemoglobin four days after starting rivaroxaban. We present possible pharmacologic explanations. We propose the idea that specific subgroups of patients may be at risk for true INR elevations and may benefit from routine monitoring of their INR while on rivaroxaban.

A Real-world Experience of the Safety and Efficacy of Non-vitamin K Oral Anticoagulants Versus Warfarin in Patients with Non-valvular Atrial Fibrillation— A Single-centre Retrospective Cohort Study in Singapore

Introduction: Non-vitamin K oral anticoagulants (NOACs) were shown to have better outcomes than warfarin for non-valvular atrial fibrillation (NVAF). Given limited local real-world data, this study aims to evaluate the safety and efficacy of NOACs versus warfarin for NVAF in Singapore. Methods: This single-centre retrospective cohort study included 439 patients ≥ 21 years old that were newly prescribed with oral anticoagulants (OACs) for NVAF in 2015. Follow-ups for patients upon OAC initiation lasted either for 2 years or until the occurrence of bleeding or thromboembolism event or death (whichever was earlier). Primary endpoints included major bleeding and stroke, while secondary endpoints included overall bleeding and thromboembolic events. Time-to-events was evaluated via Kaplan-Meier survival analysis. Data on time in therapeutic range (TTR) and compliance were analysed. Results: Patients were assigned to 4 groups: warfarin (157, 35.8%), rivaroxaban (154, 35.1%), apixaban (98, 22.3%) and dabigatran (30, 6.8%). With a mean age of 70.8 (±10.8) years old, the population were predominantly males (56.5%) and comprised Chinese (73.8%), Malays (18.7%) and others (7.5%). The rates of stroke per year were 0.7%, 1.7%, 2.2% and 0% for warfarin, rivaroxaban, apixaban and dabigatran, respectively (P=0.411), whereas those of major bleeding were 2.7%, 1.4%, 2.2% and 0% (P=0.560). As compared to warfarin, no significant differences were observed for risks of stroke and of major bleeding for rivaroxaban (adjusted hazard ratio (HR) 4.19, 95% confidence interval (CI) 0.68–26.05, P=0.124 and adjusted HR 0.43, 95% CI 0.12–1.59, P=0.207) and apixaban (adjusted HR 5.33, 95% CI 0.85–33.34, P=0.074 and adjusted HR 1.54, 95% CI 0.39–6.15, P=0.538). Mean TTR was 68.8% (±24.3%) for warfarin. Compliance rates for rivaroxaban, apixaban, and dabigatran were 56.6%, 59.2%, and 44.8% respectively (P=0.177). Conclusion: NOACs were associated with similar stroke and major bleeding rates as warfarin for NVAF. Keywords: Anticoagulant, Asian, atrial fibrillation, compliance, haemorrhage, thrombosis

Anti-Factor Xa Activity of Standard and Japan-Specific Doses of Rivaroxaban in Thai Patients With Non-Valvular Atrial Fibrillation

BACKGROUND

Recommended rivaroxaban doses for stroke prevention in atrial fibrillation (SPAF) are 20 and 15 mg/day in patients with normal and reduced renal function, respectively, but lower doses (15 and 10 mg) have been tested and approved in Japan. It is not known whether 15 and 10 mg rivaroxaban are appropriate in other Asian populations. This study compared the anti-Factor Xa (FXa) activity of 20 and 15 mg rivaroxaban in Thai patients with normal renal function and 15 and 10 mg rivaroxaban in patients with reduced renal function.

METHODS AND RESULTS

Sixty non-valvular atrial fibrillation patients receiving rivaroxaban (mean [±SD] age 69.3±9.1 years, mean creatinine clearance 59.2±22.7 mL/min) were enrolled. The anti-FXa activity of standard rivaroxaban and Japan-specific doses was measured at peak and trough concentrations. Median anti-FXa activity at peak concentrations was significantly higher for the standard than Japan-specific dose. Median anti-FXa activity measured at the trough was significantly higher for the standard dose only in those with impaired renal function. A higher proportion of patients receiving the Japan-specific rather than standard dose had anti-FXa activity at peak concentrations within the expected range (87.7% vs. 64.4%; P=0.001). One-third of those receiving the standard dose had anti-FXa activity higher than the expected range.

CONCLUSIONS

A significantly higher proportion of Thai patients receiving the Japan-specific dose of rivaroxaban had anti-FXa activity at peak concentrations within the expected range.

Efficacy and safety of direct oral anticoagulants versus low-molecular-weight heparin in patients with cancer: a systematic review and meta-analysis

The efficacy and safety of direct oral anticoagulants (DOACs) versus low-molecular-weight heparin (LMWH) are still debated in the treatment of patients with cancer, and the optimal duration of therapy remains uncertain. Electronic databases (PubMed, Embase, and Cochrane Library) were searched to retrieve studies on the efficacy and safety of DOACs versus LMWH in treating patients with cancer from January 1980 to October 2018. The primary efficacy and safety endpoints were recurrent venous thromboembolism (VTE) and major bleeding. Our study included two randomized controlled trials (RCTs) and nine observational studies, together comprising 4509 patients with cancer. The pooled estimates indicated that DOACs led to a modest reduction recurrent VTE in the RCTs [RR: 0.63, 95% confidence interval (CI), 0.42-0.96, P = 0.03] and in the observational studies (RR: 0.74, 95% CI, 0.58-0.93, P = 0.011), without increasing the risk of major bleeding for observational studies (P = 0.805), but increased for RCTs (P = 0.017). The same trends were observed in the rivaroxaban subgroup. Moreover, subgroup analyses according to the treatment duration indicated that DOACs significantly reduced the incidence of recurrent VTE (P = 0.006 at 6 months; P < 0.001 at 12 months) without significant differences in major bleeding compared with LMWH at 6 or 12 months. Patients with cancer who received DOACs exhibited a significant reduction in recurrent VTE with no increased risk of major bleeding compared with LMWH. DOACs may be an alternative choice for long-term anticoagulant therapy in patients with cancer.

Comparison of two point of care whole blood coagulation analysis devices and conventional coagulation tests as a predicting tool of perioperative bleeding in adult cardiac surgery-a pilot prospective observational study in Japan

BACKGROUND

It is widely accepted that Point-of Care Test (PoCT) devices are useful in the detection of coagulopathies in situations of massive bleeding such as major cardiac surgery. These devices contribute to the reduction of blood transfusion. However, their implementation remains limited in Japan because of their cost and lack of health insurance support.

STUDY DESIGN AND METHODS

Conventional coagulation tests and thromboelastography (TEG)/Sonoclot values were measured in 50 consecutive cardiac surgery cases. Clinical background information such as operative procedures was obtained from electronic medical records, and the theoretical perioperative total blood loss was calculated by measuring the hemoglobin content and total red blood cell transfusion volume. The correlation between perioperative total blood loss and the measured laboratory values or clinical parameters was evaluated by a multivariate linear regression analysis. The risk factors of the total amount of platelet transfusion and postoperative drain bleeding volume were similarly evaluated.

RESULTS

No significant association between the estimated perioperative total blood loss (eTBL) and the laboratory measurements including conventional coagulation tests, TEG and Sonoclot was observed. On the other hand, postoperative drain bleeding volume was significantly associated with postoperative Sonoclot CR (p = 0.039) as well as preoperative use of oral anticoagulants and cell saver treated blood volume. Platelet transfusion amount was significantly associated with post-CBP PF and time to peak value of Sonoclot (p = 0.014 and 0.001, respectively).

CONCLUSION

Sonoclot measurements may be useful to estimate the risks of postoperative bleeding and platelet transfusion in cardiac surgeries in Japan.

Real-World Rivaroxaban and Apixaban Levels in Asian Patients With Atrial Fibrillation

This study aims to measure the plasma levels of rivaroxaban and apixaban among Asian patients with atrial fibrillation and compare the results with expected drug levels from clinical studies. A total of 73 patients taking rivaroxaban and 105 patients taking apixaban were enrolled. Peak and trough levels were measured using ultra-high performance liquid chromatography with tandem mass spectrometry. The percentage of those with drug levels within the expected range reported in clinical studies was significantly higher in the apixaban group than in the rivaroxaban group, both for trough (84.8% vs. 64.4%; P = 0.002) and peak levels (76.9% vs. 33.8%; P < 0.001). After adjusting for age, sex, kidney function, appropriate dose, and adherence, patients taking rivaroxaban were still less likely to have peak and trough levels within the expected drug levels. Our real-world data suggests that Asian patients taking rivaroxaban are more likely to have out-of-expected drug levels than those taking apixaban.

Incidence of thromboembolic and bleeding events in patients with newly diagnosed nonvalvular atrial fibrillation: An Asian multicenter retrospective cohort study in Singapore

BACKGROUND

Real-world effectiveness and safety of antithrombotics in nonvalvular atrial fibrillation (NVAF) patients in Singapore has not been thoroughly studied.

HYPOTHESIS

Users of various antithrombotics experience a significantly different risk of stroke and major bleed compared with warfarin users.

METHODS

This multicenter retrospective cohort study included patients age ≥ 21 years newly diagnosed with NVAF between July 2012 and September 2015. Using electronic medical records, data on patients' demographics, antithrombotics prescribed, and CHA₂ DS₂ -VASc and HAS-BLED risk factors were collected. Patients were followed for 1 year from diagnosis for the primary effectiveness and safety endpoints of incident stroke or systemic embolism and major bleed, respectively. The secondary safety endpoint was overall bleed. Hazard ratios (HR) were determined from Cox regression.

RESULTS

Of 743 patients included, 224 were on warfarin, 156 on direct oral anticoagulants (DOACs), 277 on single antiplatelet therapy (SAPT), 28 on dual antiplatelet therapy (DAPT), and 58 on no therapy. Mean age (±SD) was 68.7 ± 13.0 years. Compared with warfarin users, SAPT (adjusted [adj.] HR: 3.70, 95% confidence interval [CI]: 1.21-11.3) and DAPT users (adj. HR: 10.1, 95% CI: 1.51-67.2) were more likely to develop thromboembolic outcomes. Also, DOAC users (adj. HR: 0.304, 95% CI: 0.158-0.585), SAPT users (adj. HR: 0.142, 95% CI: 0.0680-0.295), and DAPT users (adj. HR: 0.112, 95% CI: 0.0146-0.857) were less likely to experience any bleed compared with warfarin users.

CONCLUSIONS

SAPT and DAPT are less effective than warfarin in NVAF patients. DOACs may be considered in view of lower risk of overall bleed.