Abstract
Background
Current guidelines recommend factor IIa- or Xa-specific inhibitors over warfarin analogs for preventing thromboembolic stroke in patients with atrial fibrillation (AF). However, their plasma concentrations in Korean patients are not well understood.
Methods
We conducted a single-center laboratory study to determine the distribution ranges of peak and trough concentrations of three factor Xa inhibitors (apixaban, edoxaban, and rivaroxaban) prescribed for preventing strokes in patients with AF. Patients receiving one of these drugs and undergoing blood specimen collection for laboratory tests were screened. Blood specimens were obtained from patients who had adhered to the prescribed drug regimen consistently for at least 1 week. Drug plasma concentrations were measured using heparin liquid-reagent technology-based anti-Xa chromogenic assays.
Results
We selected 459 patients who were taking standard or on-label-reduced doses of apixaban (N=252), edoxaban (N=182), or rivaroxaban (N=25). The 5th–95th percentile ranges of the peak concentrations were 84–414 ng/mL (apixaban), 72–424 ng/mL (edoxaban), and 97–517 ng/mL (rivaroxaban). The respective 5th–95th percentile ranges of the trough concentrations were 44–237 ng/mL, 23–93 ng/mL, and 13–219 ng/mL. Approximately 19.6% (apixaban), 33.3% (edoxaban), and 64.0% (rivaroxaban) of patients in each group had peak concentrations out of the predicted distribution ranges based on pharmacokinetic data. Approximately 7.3%, 52.8%, and 8.3% of patients had trough concentrations out of the predicted distribution ranges.
Conclusions
A considerable proportion of Korean patients with AF taking factor Xa inhibitors may require population-specific reference ranges to guide therapeutic monitoring.
Keywords: Atrial fibrillation, Concentration, Factor Xa inhibitors, Plasma
INTRODUCTION
Current guidelines from the Korean Heart Rhythm Society and other major cardiology societies recommend a direct oral anticoagulant (DOAC) for preventing strokes in patients with atrial fibrillation (AF), except for those with a mechanical valve or advanced mitral valve stenosis [1]. Four DOACs (including one factor IIa inhibitor and three factor Xa inhibitors) are clinically available. Apixaban, edoxaban, and rivaroxaban are factor Xa inhibitors prescribed worldwide for preventing thromboembolic stroke in patients with non-valvular AF [2–4].
Pharmacokinetic data for the predicted distribution ranges of steady-state DOAC concentrations were acquired mainly from phase II and III trials [5–10]. The results of previous phase III trials (ARISTOTLE, ENGAGE AF-TIMI 48, and ROCKET-AF) demonstrated the general efficacy and safety of apixaban, edoxaban, and rivaroxaban. However, only 16.0%, 16.0%, and 7.5% of the respective patients were Asian [2–4]. In these studies, only 31.8%, 32.1%, and 1.1% of the enrolled patients underwent pharmacokinetic studies for drug concentration measurements [5–7]. The predicted distribution ranges, mainly derived from pharmacokinetic data acquired from these phase III trials, may not reflect the actual drug concentrations in Asian patients. Furthermore, the clinical characteristics of Asian patients encountered in real-world practice may differ considerably from those enrolled in the phase III trials. Pharmacokinetic real-world data for the factor Xa inhibitor concentrations in Asian patients are even sparser [8–10].
Although current guidelines do not recommend routine laboratory measurements of DOAC concentrations, these data can provide additional information to clinicians when assessing patient adherence to drug therapy, evaluating suspected clinically relevant drug–drug interactions, or managing specific patients with unusual medical conditions who are usually excluded from phase III trials. However, the distribution ranges of DOAC concentrations in Korean patients with non-valvular AF have not been well studied. We conducted a single-center laboratory study to determine the distribution ranges of peak and trough concentrations of apixaban, edoxaban, and rivaroxaban, which are widely prescribed for preventing thromboembolic stroke in routine clinical practice.
MATERIALS AND METHODS
Patient screening, patient selection criteria, and ethical review
This study was designed as a single-center, observational, cross-sectional laboratory study to evaluate the plasma concentrations of three factor Xa inhibitors in Korean patients with AF. The study protocol was reviewed and approved by the Institutional Review Board of Dong-A University Hospital, Busan, Korea (approval number: DAUHIRB-21-019). Informed consent was waived under the approval of the Institutional Review Board, as only excess blood specimens (remaining after conducting routine laboratory tests) were used for the study.
We screened patients with non-valvular AF who were taking one of three factor Xa inhibitors (apixaban, edoxaban, or rivaroxaban) and undergoing blood specimen collection for routine laboratory tests from April 1, 2021, to December 31, 2022, in the arrhythmia clinic of Dong-A University Hospital, Busan, Korea, for enrollment in this study. We included patients taking a factor Xa inhibitor at a standard dose or an on-label-reduced dose according to the practice guidelines for AF management recommended by the Korean Heart Rhythm Society [1]. The number of patients enrolled in our study was determined based on the availability of chromogenic assay reagents for measuring DOAC concentrations. We screened 557 Korean patients taking a factor Xa inhibitor and undergoing blood specimen collection for routine laboratory tests. Among the screened patients, 502 were taking a factor Xa inhibitor at a standard dose or an on-label-reduced dose. Twenty-nine patients who had taken a moderate-to-high dose of amiodarone for cardioversion and six patients with end-stage renal disease were excluded from the analysis. Another eight patients were excluded from trough concentration measurements owing to delayed blood specimen collection. Finally, 459 patients were selected for further analysis and divided into three groups: apixaban (N=252), edoxaban (N=182), and rivaroxaban (N=25).
For apixaban, the standard dose was 5 mg twice daily, and the on-label-reduced dose was 2.5 mg twice daily with a single-dose reduction criterion (creatinine clearance measured using the Cockcroft–Gault equation (15–30 mL/min) or multiple dose-reduction criteria (two or more of the following: age ≥80 yrs, body weight ≤60 kg, or creatinine ≥1.5 mg/dL). For edoxaban, the standard dose was 60 mg once daily, and the on-label-reduced dose was 30 mg once daily with at least one of the following dose-reduction criteria: creatinine clearance measured using the Cockcroft–Gault equation, 15–50 mL/min; body weight ≤60 kg; or concurrent use of a strong P-glycoprotein inhibitor, such as dronedarone. For rivaroxaban, the standard dose was 20 mg once daily, and the on-label-reduced dose was 15 mg once daily with a single-dose reduction criterion of creatinine clearance measured using the Cockcroft–Gault equation: 15–50 mL/min [1].
We excluded patients taking a factor Xa inhibitor at an off-label (higher or lower) dose. Patients with end-stage renal disease (defined as creatinine clearance measured using the Cockcroft–Gault equation as <15 mL/min or requiring dialysis) or those with advanced liver disease (Child–Turcotte–Pugh, category B or C) were excluded. Patients taking at least one antiplatelet agent concomitantly (including acetylsalicylic acid) at the time of blood specimen collection were also excluded. Patients taking a moderate-to-high dose of amiodarone (>200 mg/day) for at least 1 day within the 1-month period before blood specimen collection were excluded to minimize potential drug–drug interactions, considering amiodarone’s long half-life. However, patients receiving a low dose of amiodarone (≤200 mg/day) or the standard dose of dronedarone (400 mg twice daily) were eligible for inclusion in the absence of concomitant use of moderate-to-strong P-glycoprotein inhibitor(s).
Blood specimen collection
In cases where the morning dose was omitted on the day of blood specimen collection, the corresponding blood specimen was used to determine the trough concentration. The patient was recommended to take the morning dose after initial blood specimen collection and to undergo a second blood specimen collection 2–3 hrs later, using a blood specimen collection device with an indwelling needle. The second blood specimen was used to measure the relevant peak concentration. Trough concentrations were not measured when the time interval from the last drug intake to blood specimen collection was ≥16 hrs for apixaban or ≥28 hrs for edoxaban and rivaroxaban. In cases where the time interval from the morning dose intake to blood specimen collection was ≥180 min, the specimens were not processed for peak concentration measurements.
Laboratory measurements of factor Xa inhibitor concentrations
Peripheral blood specimens were collected using VACUETTE blood-collection tubes containing 3.2% sodium citrate (Greiner Bio-One, GmbH, Frickenhausen, Germany) and centrifuged at 1,518×g (3,000 rpm) for 15 min immediately after collection. Plasma specimens were stored frozen at −20°C until analysis. These conditions are consistent with the recommendations of the International Council for Standardization in Hematology. All specimens were in excess after the prothrombin time (PT) or activated partial thromboplastin time tests were completed. Stored plasma specimens were processed within 1 week after blood specimen collection. Plasma concentrations of factor Xa inhibitors were measured in heparin liquid-reagent technology (LRT)-based anti-Xa chromogenic assays, using test reagents (BIOPHENTM Heparin LRT, HYPHEN BioMed, Neuville-sur-Oise, France) specific for apixaban, edoxaban, and rivaroxaban, on a Sysmex CS-5100 Coagulation Analyzer (Sysmex Corp., Kobe, Japan).
Collection of medical information
The last intake time of the prescribed drug and adherence to therapy were assessed during arrhythmia clinic visits through patient interviews, and responses were recorded in electronic charts by an arrhythmia specialist. Plasma specimens stored in our laboratory were processed using anti-Xa chromogenic assays when patients had received a factor Xa inhibitor for at least 1 week without missed doses or dose titration before blood specimen collection.
Medical record review and statistical analysis
The study protocol was designed by a hematopathologist. The medical records of patients whose plasma specimens underwent anti-Xa chromogenic assays were collected and sequentially reviewed by cardiology specialists in imaging and arrhythmia, after which appropriate data were finally selected. The completeness of the collected data was confirmed by a neurology (stroke) specialist. The data were analyzed by a professional statistician. Continuous variables are presented as means±2 SDs, and categorical variables are presented as the number of cases with percentages. All statistical analyses were performed using IBM SPSS Statistics, version 21.0 (IBM Corp., Armonk, NY, USA), and dot plot figures were generated using MedCalc, version 19.6 (MedCalc Software Ltd., Ostend, Belgium).
RESULTS
Study patients
Clinical characteristics of the patients were generally similar between the groups. These characteristics included age, sex, body weight, creatinine clearance (measured using the Cockcroft–Gault equation), CHA2DS2-VASc score, a modified HAS-BLED score, and comorbidities. More patients in the apixaban and edoxaban groups (approximately 40%) had a low body weight (≤60 kg). The proportion of patients with moderate renal dysfunction (defined as a creatinine clearance of 15–50 mL/min, measured using the Cockcroft–Gault equation) was high in all groups, at approximately 30%. Sixty-nine (15%) patients were taking a low dose of amiodarone (≤200 mg/day) or a standard dose of dronedarone (400 mg, twice daily). The patients’ clinical characteristics are summarized in Table 1.
Table 1. Clinical characteristics of the studied patients.
| Variable | Apixaban | Edoxaban | Rivaroxaban |
|---|---|---|---|
| No. patients | 252 | 182 | 25 |
| Age, yrs | 69±11 | 70±10 | 71±10 |
| Female sex, N (%) | 105 (41.7) | 69 (37.9) | 8 (32.0) |
| Atrial fibrillation status | |||
| Paroxysmal, N (%) | 156 (61.9) | 98 (53.8) | 6 (24.0) |
| Persistent, N (%) | 53 (21.0) | 28 (15.4) | 9 (36.0) |
| Permanent, N (%) | 43 (17.1) | 56 (30.8) | 10 (40.0) |
| Body weight, kg | 66±13 | 66±11 | 70±11 |
| Body weight ≤60 kg, N (%) | 101 (40.0) | 69 (37.9) | 5 (20.0) |
| Laboratory finding | |||
| Creatinine, µmol/L | 88.4±35.4 | 88.4±26.5 | 92.8±30.1 |
| CrCl, mL/min | 63±27 | 62±21 | 57±22 |
| CrCl ≤50 mL/min, N (%) | 81 (32.1) | 53 (29.1) | 9 (36.0) |
| CrCl ≤30 mL/min, N (%) | 27 (10.7) | 13 (7.1) | 2 (8.0) |
| Hemoglobin, g/L | 138.0±65.0 | 133.0±16.0 | 134.0±22.0 |
| Platelets, 109/L | 211±66 | 208±53 | 212±59 |
| PT, sec | 13.0±1.2 | 13.0±1.8 | 13.5±1.8 |
| aPTT, sec | 28.7±2.7 | 31.6±4.0 | 36.7±4.8 |
| Comorbid disease | |||
| Hypertension, N (%) | 105 (41.7) | 73 (40.1) | 12 (48.0) |
| Diabetes mellitus, N (%) | 64 (25.4) | 50 (27.5) | 8 (32.0) |
| Heart failure, N (%) | 93 (36.9) | 67 (36.8) | 12 (48.0) |
| CAOD/PAOD, N (%) | 35 (13.9) | 20 (11.0) | 4 (16.0) |
| Ischemic stroke/TIA/SE, N (%) | 52 (20.6) | 31 (17.0) | 3 (12.0) |
| Bleeding event(s), N (%) | 23 (9.1) | 9 (4.9) | 1 (4.0) |
| CHA2DS2-VASc score* | 2.8±1.7 | 2.8±1.6 | 2.8±1.7 |
| Modified HAS-BLED score† | 1.5±1.0 | 1.3±0.8 | 1.4±0.8 |
| Co-administered medications | |||
| Median number (IQR) | 5 (3–7) | 4 (2–6) | 5 (3–7) |
| Mean±2 SD‡ | 5.4±3.2 | 4.5±3.0 | 4.9±3.1 |
| Statin, N (%) | 118 (46.8) | 102 (56.0) | 16 (64.0) |
| P-glycoprotein inhibitor§, N (%) | 31 (12.3) | 33 (18.1) | 5 (20.0) |
*CHA2DS2-VASc score: C, congestive heart failure; H, hypertension; A2, age ≥75 yrs; D, diabetes mellitus; S2, prior stroke, transient ischemic attack, or thromboembolism; V, vascular disease; A, age of 65–74 yrs; Sc, sex category (female). A2 and S2 were assigned 2 points each, whereas the other components were assigned 1 point each. The total score was calculated by summing these values.
†Modified HAS-BLED score: H, hypertension; A, abnormal renal or liver function (1 point each); S, history of stroke; B, history of bleeding or predisposition to bleeding; E, elderly (age >65 yrs); D, concomitant use of drugs predisposing to bleeding (e.g., antiplatelets or NSAIDs) or excessive alcohol use (1 point each). The total score was calculated by summing these values.
‡Continuous variables are presented as means±2 SDs. Categorical variables are presented as numbers with percentages.
§The P-glycoprotein inhibitors involved were amiodarone (≤200 mg/day) or dronedarone (800 mg/day). All patients in the rivaroxaban group took amiodarone but not dronedarone.
Abbreviations: CrCl, creatinine clearance measured using the Cockcroft–Gault equation; PT, prothrombin time; aPTT, activated partial thromboplastin time; CAOD, coronary artery obstructive disease; PAOD, peripheral artery obstructive disease; TIA, transient ischemic attack; SE, systemic embolism; IQR, interquartile range.
Peak and trough plasma concentration ranges of factor Xa inhibitors
Pharmacokinetic data for the predicted distribution ranges of the steady-state plasma concentrations of factor Xa inhibitors were acquired mainly from the phase II and III trial data. Population-based pharmacokinetic reports showed that the 5th–95th percentile ranges of the respective peak and trough concentrations were 69–321 ng/mL and 34–230 ng/mL for apixaban [5, 11], 101–288 ng/mL and 12–43 ng/mL for edoxaban [6, 12], and 178–343 ng/mL and 12–137 ng/mL for rivaroxaban [7, 13]. As pharmacokinetic data were not available for the Korean population, we adapted the practice guidelines for AF management of the Korean Heart Rhythm Society and the above values to derive the predicted distribution ranges of the factor Xa inhibitor concentrations. We adapted those values as reference ranges for comparisons with our data (Table 2 and Fig. 1).
Table 2. Plasma concentrations of the three factor Xa inhibitors studied.
| Variables | Apixaban | Edoxaban | Rivaroxaban |
|---|---|---|---|
| Peak concentrations of factor Xa inhibitors | |||
| No. specimens | 230 | 147 | 25 |
| Standard dose, N (%) | 190 (82.6) | 93 (63.3) | 19 (76.0) |
| On-label-reduced dose, N (%) | 40 (17.4) | 54 (36.6) | 6 (24.0) |
| Time from intake to specimen collection, min | 140±2 | 137±16 | 133±23 |
| 5th–95th percentile range, ng/mL | 84–414 | 72–424 | 97–517 |
| Predicted 5th–95th percentile range*, ng/mL | 69–321 | 101–288 | 178–343 |
| Mean±2 SD, ng/mL† | 229±105 | 222±102 | 311±136 |
| Median (IQR), ng/mL | 214 (151–290) | 212 (142–280) | 317 (182–427) |
| Higher than the predicted range, N (%) | 40 (17.4) | 35 (23.8) | 11 (44.0) |
| Lower than the predicted range, N (%) | 5 (2.2) | 14 (9.5) | 5 (20.0) |
| Within the predicted range, N (%) | 185 (80.4) | 98 (66.7) | 9 (36.0) |
| Trough concentrations of factor Xa inhibitors | |||
| No. specimens | 244 | 163 | 24 |
| Standard dose, N (%) | 198 (81.1) | 101 (62.0) | 18 (75.0) |
| On-label-reduced dose, N (%) | 46 (18.9) | 62 (38.0) | 6 (25.0) |
| Time from intake to specimen collection, hrs | 13.4±1.3 | 25.3±1.1 | 25.2±1.4 |
| 5th–95th percentile range, ng/mL | 44–237 | 23–93 | 13–219 |
| Predicted 5th–95th percentile range*, ng/mL | 34–230 | 12–43 | 12–137 |
| Mean±2 SD, ng/mL† | 122±57 | 50±25 | 67±54 |
| Median (IQR), ng/mL | 111 (85–151) | 45 (35–57) | 60 (29–83) |
| Higher than the predicted range, N (%) | 14 (5.7) | 86 (52.8) | 2 (8.3) |
| Lower than the predicted range, N (%) | 4 (1.6) | 0 (0)‡ | 0 (0)‡ |
| Within the predicted range, N (%) | 226 (92.7) | 77 (47.2) | 22 (91.7) |
*The 5th–95th percentile ranges, obtained from population-based pharmacokinetic studies and adapted to the practice guidelines for atrial fibrillation management of the Korean Heart Rhythm Society, were used as reference ranges to estimate the percentages of patients with values out of range.
†Continuous variables are presented as the mean±2 SDs. Categorical variables are presented as numbers with percentages.
‡Trough concentrations below the analytical measurement ranges could not be measured accurately.
Abbreviation: IQR, interquartile range.
Fig. 1. Peak and trough concentrations of the factor Xa inhibitors. Approximately 19.6% (apixaban group), 33.3% (edoxaban group), and 64.0% (rivaroxaban group) of patients had peak concentrations out of the predicted distribution ranges. Approximately 7.3%, 52.8%, and 8.3% had trough concentrations out of the respective predicted distribution ranges. The red and blue numbers represent the predicted 5th–95th percentile ranges of peak and trough concentrations, obtained from population-based pharmacokinetic data and adapted to the practice guidelines for atrial fibrillation management of the Korean Heart Rhythm Society. The black numbers with percentages represent the proportions of patients with factor Xa inhibitor concentrations above, within, and below the predicted 5th–95th percentiles, as indicated. Trough concentrations below the analytical measurement ranges could not be measured in the edoxaban and rivaroxaban groups.
Peak and trough plasma concentrations of the factor Xa inhibitor were measured in 87.6% and 93.9% of the respective studied patients. The 5th–95th percentile distribution ranges of the peak concentrations were 84–414 ng/mL (apixaban), 72–424 ng/mL (edoxaban), and 97–517 ng/mL (rivaroxaban), respectively.
The 5th–95th percentile distribution ranges of the trough concentrations were 44–237 ng/mL, 23–93 ng/mL, and 13–219 ng/mL, respectively. According to the manufacturer, the analytical measurement ranges for standard calibration were 15–617 ng/mL (apixaban), 23–916 ng/mL (edoxaban), and 13–525 ng/mL (rivaroxaban), respectively. A few high-concentration specimens were pre-diluted with pooled normal plasma. The peak concentrations under standard vs. on-label-reduced dosing conditions were 239±107 ng/mL vs. 183±83 ng/mL (P=0.001) in the apixaban group, 244±106 ng/mL vs. 184± 82 ng/mL (P<0.001) in the edoxaban group, and 307±132 ng/mL vs. 321±163 ng/mL (P=0.854) in the rivaroxaban group. The trough concentrations under standard vs. on-label-reduced dosing conditions were 123±55 ng/mL vs. 119±63 ng/mL (P=0.651) in the apixaban group, 50±23 ng/mL vs. 48±29 ng/mL (P=0.647) in the edoxaban group, and 61±42 ng/mL vs. 86±82 ng/mL (P=0.497) in the rivaroxaban group.
The 5th–95th percentile values of the peak and trough concentrations were widely distributed in relatively higher ranges than the predicted distributed ranges. The mean values±2 SDs and median values with interquartile ranges are summarized in Table 2. The plasma concentrations of apixaban, edoxaban, and rivaroxaban under standard and on-label-reduced dosing conditions are shown in Fig. 1. Approximately 19.6% (apixaban), 33.3% (edoxaban), and 64.0% (rivaroxaban) of the patients in each group had peak concentrations out of the predicted distribution ranges. Approximately 7.3%, 52.8%, and 8.3% of the patients in each respective group had trough concentrations out of the predicted distribution ranges. The peak or trough plasma concentrations of patients taking medication once daily (edoxaban or rivaroxaban) were more frequently out of the predicted distribution ranges than those taking medication twice daily (apixaban). In all factor Xa inhibitor groups, the proportion of patients with peak and trough concentrations above the predicted distribution ranges was consistently higher than that of patients with concentrations lower than the predicted distribution ranges.
DISCUSSION
We evaluated 459 patients with non-valvular AF who were taking a factor Xa inhibitor at a standard or on-label-reduced dose for stroke prevention. The 5th–95th percentile values of the peak and trough concentrations of factor Xa inhibitors were distributed in relatively higher ranges than the predicted distributed ranges of all factor Xa groups. Among the three factor Xa inhibitor groups, the distribution range of apixaban concentrations most closely aligned with the predicted ranges reported in previous population-based pharmacokinetic studies. In contrast, edoxaban concentrations exhibited higher distribution ranges than predicted. Although the peak concentrations in the rivaroxaban group also appeared elevated, similar to those of edoxaban, the trough concentrations remained within the predicted distribution ranges. However, the number of rivaroxaban concentrations analyzed was too small to determine the exact distribution ranges of the drug.
The reasons why the 5th–95th percentile ranges of the factor Xa inhibitor concentrations in Korean patients differed from those predicted by population-based pharmacokinetic studies are unclear. However, the following explanations can be considered. First, the co-existence of multiple dose-reduction criteria may have influenced the factor Xa inhibitor concentrations. In previous phase III studies for apixaban and edoxaban, 2.3% and 9.7% of patients, respectively, had a low body weight (≤60 kg) [2, 3]. In this study, 40.0% and 37.9% of patients taking apixaban or edoxaban, respectively, had a low body weight. In those phase III studies for apixaban and edoxaban, 16.5% and 19.6% of the patients exhibited moderate renal dysfunction (creatinine clearance ≤50 mL/min), respectively [2, 3]. In this study, 32.1% and 29.1% of patients taking the corresponding drugs had moderate renal dysfunction. A relatively higher proportion of patients with multiple dose-reduction criteria showed higher peak and trough concentrations than expected based on the predicted distribution ranges. Second, the metabolism of factor Xa inhibitors might differ between Asian and Western populations. The East Asian paradox, characterized by weaker anti-thrombotic effects of clopidogrel or warfarin analogs with a higher bleeding risk, has been at least partially explained by drug-metabolism differences between East Asian and Western populations [14]. Third, undiscovered drug–drug interactions with concomitant drugs, herbal medications, or dietary supplements, which were not investigated in detail here, may have influenced the metabolism of factor Xa inhibitors. Finally, different methods for measuring factor Xa inhibitor concentrations may have resulted in variability in the results. Directly measuring DOAC concentrations using HPLC coupled with mass spectrometry (LC/MS) is still considered the gold standard method by laboratory medicine specialists [15]. We measured drug concentrations using heparin LRT-based factor Xa chromogenic assays. Although prior laboratory reports demonstrated a close correlation of factor Xa concentrations measured using two technically different methods [16, 17], the possibility that technical differences led to differing results cannot be excluded.
Current guidelines from major cardiology societies suggest that DOAC concentrations can be measured in critical situations, such as major bleeding, emergent surgery, stroke, and drug overdose [18]. Under certain conditions where DOAC concentrations may be unpredictable (e.g., poor drug adherence or substantial drug–drug interactions) or in patient populations usually excluded from phase III trials (e.g., patients with substantially low or high body weight or patients with end-stage renal disease), assessing DOAC concentrations to minimize continuous exposure to extremely high or low concentrations may be reasonable. In addition, the clinical characteristics of patient populations encountered in real-world practice may differ considerably from those enrolled in randomized controlled trials [19]. Many older Korean patients meeting multiple dose-reduction criteria use both anticoagulants and herbal medications containing several dietary supplements. Using a heparin LRT-based anti-Xa chromogenic assay as a point-of-care test can provide useful information on the patient’s DOAC concentration.
The relationship between DOAC concentrations and clinical events is controversial [20–22]. Large population-based pharmacokinetic reports have indicated that higher edoxaban trough concentrations are related to higher calculated incidences of major bleeding and intracerebral hemorrhage, but that they are also related to lower calculated incidences of stroke and systemic embolism [23, 24]. The clinical utility of chromogenic assay-based DOAC concentration measurements with subsequent dose adjustment should be verified in future studies. However, measuring DOAC concentrations as a point-of-care test may provide physicians with a better understanding of the patient’s medical conditions and enable opportunities for reducing anticoagulation-related complications via patient-tailored clinical decision-making. Although LC/MS is considered the gold standard for measuring DOAC concentrations, its technical complexity, prolonged processing time, and requirement for expensive laboratory equipment and laboratory personnel limit its applicability in clinical practice. The absence of international standards for calibration and standardizing assay results is another limitation of LC/MS. The heparin LRT-based universal anti-Xa chromogenic assay enables rapid quantification of DOAC concentrations, delivering accurate results within 1–2 hrs of blood specimen collection by employing automated coagulation analyzers and standardized, drug-specific calibration reagents, thereby facilitating clinical utility. However, anti-Xa chromogenic assay-driven pharmacokinetic data are insufficient and should be supplemented to provide physicians with appropriate clinical information.
Our results should be interpreted cautiously for the following reasons. First, the study patients do not necessarily represent the general characteristics of Korean or Asian patients with AF who are taking factor Xa inhibitors. Only a small number of patients in a single tertiary hospital were selected for this study, and the number of patients in the rivaroxaban group was too small to define exact distribution ranges for the drug. Second, the possibility exists that selection bias occurred for frail patients or those at high risk for AF. Blood specimens from patients who underwent routine laboratory tests during the limited screening period were acquired. Patients at high risk for AF with multiple dose-reduction criteria or frail patients with minor bleeding events due to repeated laboratory tests of specimens might have undergone more frequent testing. Third, the measured values cannot represent the average concentrations of a specific patient due to potential intra-individual differences. Prior data demonstrated significant intra-individual differences in DOAC concentrations between repeated measurements [25]. Fourth, information on drug adherence and intake timing (which may have influenced the factor Xa inhibitor concentrations) may have been inaccurate, considering that these data were obtained through patient recall and self-reporting. Such information should be collected by an electrophysiologist during a short patient interview in an outpatient clinic setting. Information about concomitant medications, herbal medications, dietary supplements, and factor Xa intake times could not be investigated thoroughly owing to the limited time available for collecting detailed patient histories. Fifth, as discussed earlier, factor Xa concentrations were measured using heparin LRT-based factor Xa chromogenic assays. Sixth, trough concentrations below the analytical measurement ranges could not be measured appropriately.
We measured 5th–95th percentile distribution ranges for apixaban, edoxaban, and rivaroxaban prescribed for preventing embolic stroke in Korean patients with AF under standard and on-label reduced dosing conditions. Our analysis indicates wide interindividual variability in the DOAC plasma concentrations of this population. These findings suggest that a substantial proportion of patients may have drug levels falling outside the predicted pharmacokinetic ranges and highlight the necessity of measuring DOAC plasma concentrations. Further research is required to evaluate the relationship between DOAC plasma concentrations and clinical outcomes.
ACKNOWLEDGEMENTS
We thank Sysmex Korea Co., Ltd. for providing anti-Xa Heparin LRT reagents and Kwang-Min Lee for providing statistical analysis services.
Footnotes
AUTHOR CONTRIBUTIONS
Park JS and Han JY conceived of the project. Woo KS and Han JY developed the methodology. Park JS, Lim KH, and Kim DH contributed to the investigation. Park JS and Lee KM contributed to visualization. Han JY acquired funding for the project. Park JS and Han JY contributed to project administration. Park JS and Han JY supervised the project. Park JS, Lim KH, Kim DH, Lee KM, Woo KS, and Han JY helped write the original draft. Park JS, Lim KH, Kim DH, Lee KM, Woo KS, and Han JY reviewed and edited the manuscript.
CONFLICTS OF INTEREST
None declared.
RESEARCH FUNDING
The work was supported by a National Research Foundation of Korea (NRF) grant funded by the Korean Government (MSIT; grant number 2022R1A2C1009739 to Han JY).
REFERENCES
- 1.Joung B, Lee JM, Lee KH, Kim TH, Choi EK, Lim WH, et al. 2018 Korean guideline of atrial fibrillation management. Korean Circ J. 2018;48:1033–80. doi: 10.4070/kcj.2018.0339. [DOI] [PMC free article] [PubMed] [Google Scholar]
- 2.Granger CB, Alexander JH, McMurray JJV, Lopes RD, Hylek EM, Hanna M, et al. Apixaban versus warfarin in patients with atrial fibrillation. N Engl J Med. 2011;365:981–92. doi: 10.1056/NEJMoa1107039. [DOI] [PubMed] [Google Scholar]
- 3.Giugliano RP, Ruff CT, Braunwald E, Murphy SA, Wiviott SD, Halperin JL, et al. Edoxaban versus warfarin in patients with atrial fibrillation. N Engl J Med. 2013;369:2093–104. doi: 10.1056/NEJMoa1310907. [DOI] [PubMed] [Google Scholar]
- 4.Patel MR, Mahaffey KW, Garg J, Pan G, Singer DE, Hacke W, et al. Rivaroxaban versus warfarin in nonvalvular atrial fibrillation. N Engl J Med. 2011;365:883–91. doi: 10.1056/NEJMoa1009638. [DOI] [PubMed] [Google Scholar]
- 5.Zeitouni M, Giczewska A, Lopes RD, Wojdyla DM, Christersson C, Siegbahn A, et al. Clinical and pharmacological effects of apixaban dose adjustment in the ARISTOTLE trial. J Am Coll Cardiol. 2020;75:1145–55. doi: 10.1016/j.jacc.2019.12.060. [DOI] [PubMed] [Google Scholar]
- 6.Ruff CT, Giugliano RP, Braunwald E, Morrow DA, Murphy SA, Kuder JF, et al. Association between edoxaban dose, concentration, anti-factor Xa activity, and outcomes: an analysis of data from the randomised, double-blind ENGAGE AF-TIMI 48 trial. Lancet. 2015;385:2288–95. doi: 10.1016/S0140-6736(14)61943-7. [DOI] [PubMed] [Google Scholar]
- 7.Girgis IG, Patel MR, Peters GR, Moore KT, Mahaffey KW, Nessel CC, et al. Population pharmacokinetics and pharmacodynamics of rivaroxaban in patients with non-valvular atrial fibrillation: results from ROCKET AF. J Clin Pharmacol. 2014;54:917–27. doi: 10.1002/jcph.288. [DOI] [PubMed] [Google Scholar]
- 8.Lin SY, Kuo CH, Yeh SJ, Tsai LK, Liu YB, Huang CF, et al. Real-world rivaroxaban and apixaban levels in Asian patients with atrial fibrillation. Clin Pharmacol Ther. 2020;107:278–86. doi: 10.1002/cpt.1601. [DOI] [PMC free article] [PubMed] [Google Scholar]
- 9.Goto E, Horinaka S, Ishimitsu T, Kato T. Factor Xa inhibitors in clinical practice: comparison of pharmacokinetic profiles. Drug Metab Pharmacokinet. 2020;35:151–9. doi: 10.1016/j.dmpk.2019.10.005. [DOI] [PubMed] [Google Scholar]
- 10.Yeo M, Lee SR, Choi EK, Choi J, Lee KY, Ahn HJ, et al. Plasma apixaban concentrations and thrombin generation assay parameters in response to dose reduction for atrial fibrillation. Br J Clin Pharmacol. 2024;90:3221–31. doi: 10.1111/bcp.16211. [DOI] [PubMed] [Google Scholar]
- 11.Frost C, Nepal S, Wang J, Schuster A, Byon W, Boyd RA, et al. Safety, pharmacokinetics and pharmacodynamics of multiple oral doses of apixaban, a factor Xa inhibitor, in healthy subjects. Br J Clin Pharmacol. 2013;76:776–86. doi: 10.1111/bcp.12106. [DOI] [PMC free article] [PubMed] [Google Scholar]
- 12.Steffel J, Ruff CT, Yin O, Braunwald E, Park JG, Murphy SA, et al. Randomized, double-blind comparison of half-dose versus full-dose edoxaban in 14,014 patients with atrial fibrillation. J Am Coll Cardiol. 2021;77:1197–207. doi: 10.1016/j.jacc.2020.12.053. [DOI] [PubMed] [Google Scholar]
- 13.Mueck W, Stampfuss J, Kubitza D, Becka M. Clinical pharmacokinetic and pharmacodynamic profile of rivaroxaban. Clin Pharmacokinet. 2014;53:1–16. doi: 10.1007/s40262-013-0100-7. [DOI] [PMC free article] [PubMed] [Google Scholar]
- 14.Kim HK, Tantry US, Smith SC., Jr , Jeong MH, Park SJ, Kim MH, et al. The East Asian paradox: an updated position statement on the challenges to the current antithrombotic strategy in patients with cardiovascular disease. Thromb Haemost. 2021;121:422–32. doi: 10.1055/s-0040-1718729. [DOI] [PubMed] [Google Scholar]
- 15.Gosselin RC, Adcock DM, Bates SM, Douxfils J, Favaloro EJ, Gouin-Thibault I, et al. International Council for Standardization in Haematology (ICSH) recommendations for laboratory measurement of direct oral anticoagulants. Thromb Haemost. 2018;118:437–50. doi: 10.1055/s-0038-1627480. [DOI] [PubMed] [Google Scholar]
- 16.Cini M, Legnani C, Padrini R, Cosmi B, Dellanoce C, De Rosa G, et al. DOAC plasma levels measured by chromogenic anti-Xa assays and HPLC-UV in apixaban- and rivaroxaban-treated patients from the START-Register. Int J Lab Hematol. 2020;42:214–22. doi: 10.1111/ijlh.13159. [DOI] [PubMed] [Google Scholar]
- 17.Dunois C. Laboratory monitoring of direct oral anticoagulants (DOACs) Biomedicines. 2021;9:445. doi: 10.3390/biomedicines9050445.065f4fd8d4084c34a02b197ac4526f7b [DOI] [PMC free article] [PubMed] [Google Scholar]
- 18.Steffel J, Collins R, Antz M, Cornu P, Desteghe L, Haeusler KG, et al. 2021 European Heart Rhythm Association practical guide on the use of non-vitamin K antagonist oral anticoagulants in patients with atrial fibrillation. Europace. 2021;23:1612–76. doi: 10.1093/europace/euab065. [DOI] [PMC free article] [PubMed] [Google Scholar]
- 19.Thomas A, Fang MC, Kogan S, Hubbard CC, Friedman PN, Gong L, et al. Apixaban concentrations in routine clinical care of older adults with nonvalvular atrial fibrillation. JACC Adv. 2022;1:100039. doi: 10.1016/j.jacadv.2022.100039. [DOI] [PMC free article] [PubMed] [Google Scholar]
- 20.Jakowenko N, Nguyen S, Ruegger M, Dinh A, Salazar E, Donahue KR. Apixaban and rivaroxaban anti-Xa level utilization and associated bleeding events within an academic health system. Thromb Res. 2020;196:276–82. doi: 10.1016/j.thromres.2020.09.002. [DOI] [PMC free article] [PubMed] [Google Scholar]
- 21.Mavri A, Vene N, Božič-Mijovski M, Miklič M, Söderblom L, Pohanka A, et al. Apixaban concentration variability and relation to clinical outcomes in real-life patients with atrial fibrillation. Sci Rep. 2021;11:13908. doi: 10.1038/s41598-021-93372-9.0924ed74aa5d49abbeb7d5aa319ba73a [DOI] [PMC free article] [PubMed] [Google Scholar]
- 22.Sennesael AL, Larock AS, Douxfils J, Elens L, Stillemans G, Wiesen M, et al. Rivaroxaban plasma levels in patients admitted for bleeding events: insights from a prospective study. Thromb J. 2018;16:28. doi: 10.1186/s12959-018-0183-3.1dc494086d60476894f7941f489d98be [DOI] [PMC free article] [PubMed] [Google Scholar]
- 23.Chao TF, Chen SA, Ruff CT, Hamershock RA, Mercuri MF, Antman EM, et al. Clinical outcomes, edoxaban concentration, and anti-factor Xa activity of Asian patients with atrial fibrillation compared with non-Asians in the ENGAGE AF-TIMI 48 trial. Eur Heart J. 2019;40:1518–27. doi: 10.1093/eurheartj/ehy807. [DOI] [PubMed] [Google Scholar]
- 24.Kim DH, Kwak BC, Yoon BA, Cha JK, Park JS, Kwak MS, et al. Association between plasma anti-factor Xa concentrations and large artery occlusion in patients with acute ischemic stroke taking direct oral anticoagulants for non-valvular atrial fibrillation. Ann Lab Med. 2024;44:459–62. doi: 10.3343/alm.2024.0036. [DOI] [PMC free article] [PubMed] [Google Scholar]
- 25.Toorop MMA, van Rein N, Nierman MC, Vermaas HW, Huisman MV, van der Meer FJM, et al. Inter- and intra-individual concentrations of direct oral anticoagulants: the KIDOAC study. J Thromb Haemost. 2022;20:92–103. doi: 10.1111/jth.15563. [DOI] [PMC free article] [PubMed] [Google Scholar]