Pharmacotherapeutic group: antithrombotic agents, direct thrombin inhibitors, ATC code: B01AE07.
Mechanism of action
Dabigatran etexilate is a small molecule prodrug which does not exhibit any pharmacological activity.
After oral administration, dabigatran etexilate is rapidly absorbed and converted to dabigatran by esterase-catalysed hydrolysis in plasma and in the liver. Dabigatran is a potent, competitive, reversible direct thrombin inhibitor and is the main active principle in plasma.
Since thrombin (serine protease) enables the conversion of fibrinogen into fibrin during the coagulation cascade, its inhibition prevents the development of thrombus. Dabigatran inhibits free thrombin, fibrin-bound thrombin and thrombin-induced platelet aggregation.
Pharmacodynamic effects
In-vivo and ex-vivo animal studies have demonstrated antithrombotic efficacy and anticoagulant activity of dabigatran after intravenous administration and of dabigatran etexilate after oral administration in various animal models of thrombosis.
There is a clear correlation between plasma dabigatran concentration and degree of anticoagulant effect based on phase II studies. Dabigatran prolongs the thrombin time (TT), ECT, and aPTT.
The calibrated quantitative diluted TT (dTT) test provides an estimation of dabigatran plasma concentration that can be compared to the expected dabigatran plasma concentrations. When the calibrated dTT assay delivers a dabigatran plasma concentration result at or below the limit of quantification, an additional coagulation assay such as TT, ECT or aPTT should be considered. The ECT can provide a direct measure of the activity of direct thrombin inhibitors.
The aPTT test is widely available and provides an approximate indication of the anticoagulation intensity achieved with dabigatran. However, the aPTT test has limited sensitivity and is not suitable for precise quantification of anticoagulant effect, especially at high plasma concentrations of dabigatran. Although high aPTT values should be interpreted with caution, a high aPTT value indicates that the patient is anticoagulated.
In general, it can be assumed that these measures of anti-coagulant activity may reflect dabigatran levels and can provide guidance for the assessment of bleeding risk, i.e. exceeding the 90th percentile of dabigatran trough levels or a coagulation assay such as aPTT measured at trough (for aPTT thresholds see section 4.4, table 4) is considered to be associated with an increased risk of bleeding.
Primary prevention of VTE in orthopaedic surgery
Steady state (after day 3) geometric mean dabigatran peak plasma concentration, measured around 2 hours after 220 mg dabigatran etexilate administration, was 70.8 ng/mL, with a range of 35.2-162 ng/mL (25th-75th percentile range). The dabigatran geometric mean trough concentration, measured at the end of the dosing interval (i.e. 24 hours after a 220 mg dabigatran dose), was on average 22.0 ng/mL, with a range of 13.0-35.7 ng/mL (25th-75th percentile range).
In a dedicated study exclusively in patients with moderate renal impairment (creatinine clearance, CrCL 30-50 mL/min) treated with dabigatran etexilate 150 mg QD, the dabigatran geometric mean trough concentration, measured at the end of the dosing interval, was on average 47.5 ng/mL, with a range of 29.6 - 72.2 ng/mL (25th-75th percentile range).
In patients treated for prevention of VTEs after hip or knee replacement surgery with 220 mg dabigatran etexilate once daily,
• the 90th percentile of dabigatran plasma concentrations was 67 ng/mL, measured at trough (20-28 hours after the previous dose) (see section 4.4 and 4.9),
• the 90th percentile of aPTT at trough (20-28 hours after the previous dose) was 51 seconds, which would be 1.3-fold upper limit of normal.
The ECT was not measured in patients treated for prevention of VTEs after hip or knee replacement surgery with 220 mg dabigatran etexilate once daily.
Clinical efficacy and safety
Ethnic origin
No clinically relevant ethnic differences among Caucasians, African-American, Hispanic, Japanese or Chinese patients were observed.
Clinical trials in VTE prophylaxis following major joint replacement surgery
In 2 large randomized, parallel group, double-blind, dose-confirmatory trials, patients undergoing elective major orthopaedic surgery (one for knee replacement surgery and one for hip replacement surgery) received Dabigatran etexilate 75 mg or 110 mg within 1-4 hours of surgery followed by 150 mg or 220 mg once daily thereafter, haemostasis having been secured, or enoxaparin 40 mg on the day prior to surgery and daily thereafter.
In the RE-MODEL trial (knee replacement) treatment was for 6-10 days and in the RE-NOVATE trial (hip replacement) for 28-35 days. Totals of 2,076 patients (knee) and 3,494 (hip) were treated respectively.
Composite of total VTE (including pulmonary embolism (PE), proximal and distal deep vein thrombosis (DVT), whatever symptomatic or asymptomatic detected by routine venography) and all-cause mortality constituted the primary end-point for both studies. Composite of major VTE (including PE and proximal DVT, whatever symptomatic or asymptomatic detected by routine venography) and VTE-related mortality constituted a secondary end-point and is considered of better clinical relevance.
Results of both studies showed that the antithrombotic effect of 220 mg and 150 mg dabigatran etexilate were statistically non-inferior to that of enoxaparin on total VTE and all-cause mortality. The point estimate for incidence of major VTE and VTE related mortality for the 150 mg dose was slightly worse than enoxaparin (table 13). Better results were seen with the 220 mg dose where the point estimate of Major VTE was slightly better than enoxaparin (table 13).
The clinical studies have been conducted in a patient population with a mean age > 65 years.
There were no differences in the phase 3 clinical studies for efficacy and safety data between men and women.
In the studied patient population of RE-MODEL and RE-NOVATE (5,539 patients treated), 51 % suffered from concomitant hypertension, 9 % from concomitant diabetes, 9 % from concomitant coronary artery disease and 20 % had a history of venous insufficiency. None of these diseases showed an impact on the effects of dabigatran on VTE-prevention or bleeding rates.
Data for the major VTE and VTE-related mortality endpoint were homogeneous with regards to the primary efficacy endpoint and are shown in table 13.
Data for the total VTE and all cause mortality endpoint are shown in table 14. Data for adjudicated major bleeding endpoints are shown in table 15 below.
Table 13: Analysis of major VTE and VTE-related mortality during the treatment period in the RE-MODEL and the RE-NOVATE orthopaedic surgery studies
| Trial | Dabigatran etexilate 220 mg | Dabigatran etexilate 150 mg | Enoxaparin 40 mg |
| RE-NOVATE (hip) |
| N | 909 | 888 | 917 |
| Incidences (%) | 28 (3.1) | 38 (4.3) | 36 (3.9) |
| Risk ratio over enoxaparin | 0.78 | 1.09 | |
| 95 % CI | 0.48, 1.27 | 0.70, 1.70 | |
| RE-MODEL (knee) |
| N | 506 | 527 | 511 |
| Incidences (%) | 13 (2.6) | 20 (3.8) | 18 (3.5) |
| Risk ratio over enoxaparin | 0.73 | 1.08 | |
| 95 % CI | 0.36, 1.47 | 0.58, 2.01 | |
Table14: Analysis of total VTE and all cause mortality during the treatment period in the RE-NOVATE and the RE-MODEL orthopaedic surgery studies
| Trial | Dabigatran etexilate 220 mg | Dabigatran etexilate 150 mg | Enoxaparin 40 mg |
| RE-NOVATE (hip) |
| N | 880 | 874 | 897 |
| Incidences (%) | 53 (6.0) | 75 (8.6) | 60 (6.7) |
| Risk ratio over enoxaparin | 0.9 | 1.28 | |
| 95 % CI | (0.63, 1.29) | (0.93, 1.78) | |
| RE-MODEL (knee) |
| N | 503 | 526 | 512 |
| Incidences (%) | 183 (36.4) | 213 (40.5) | 193 (37.7) |
| Risk ratio over enoxaparin | 0.97 | 1.07 | |
| 95 % CI | (0.82, 1.13) | (0.92, 1.25) | |
Table 15: Major bleeding events by treatment in the individual RE-MODEL and the RE-NOVATE studies
| Trial | Dabigatran etexilate 220 mg | Dabigatran etexilate 150 mg | Enoxaparin 40 mg |
| RE-NOVATE (hip) |
| Treated patients N | 1,146 | 1,163 | 1,154 |
| Number of MBE N(%) | 23 (2.0) | 15 (1.3) | 18 (1.6) |
| RE-MODEL (knee) |
| Treated patients N | 679 | 703 | 694 |
| Number of MBE N(%) | 10 (1.5) | 9 (1.3) | 9 (1.3) |
Clinical trials for the prevention of thromboembolism in patients with prosthetic heart valves
A phase II study examined dabigatran etexilate and warfarin in a total of 252 patients with recent mechanical valve replacement surgery (i.e. within the current hospital stay) and in patients who received a mechanical heart valve replacement more than three months ago. More thromboembolic events (mainly strokes and symptomatic/asymptomatic prosthetic valve thrombosis) and more bleeding events were observed with dabigatran etexilate than with warfarin. In the early post-operative patients, major bleeding manifested predominantly as haemorrhagic pericardial effusions, specifically in patients who started dabigatran etexilate early (i.e. on Day 3) after heart valve replacement surgery (see section 4.3).
Paediatric population
Clinical trials in VTE prophylaxis following major joint replacement surgery
The European Medicines Agency has waived the obligation to submit the results of studies with reference medicinal product in all subsets of the paediatric population in prevention of thromboembolic events for the indication of primary prevention of VTE in patients who have undergone elective total hip replacement surgery or total knee replacement surgery (see section 4.2 for information on paediatric use).
Treatment of VTE and prevention of recurrent VTE in paediatric patients
The DIVERSITY study was conducted to demonstrate the efficacy and safety of dabigatran etexilate compared to standard of care (SOC) for the treatment of VTE in paediatric patients from birth to less than 18 years of age. The study was designed as an open-label, randomised, parallel-group, non inferiority study. Patients enrolled were randomised according to a 2:1 scheme to either an age-appropriate formulation (capsules, coated granules or oral solution) of dabigatran etexilate (doses adjusted for age and weight) or SOC comprised of low molecular weight heparins (LMWH) or vitamin K antagonists (VKA) or fondaparinux (1 patient 12 years old). The primary endpoint was a composite endpoint of patients with complete thrombus resolution, freedom from recurrent VTE, and freedom from mortality related to VTE. Exclusion criteria included active meningitis, encephalitis and intracranial abscess.
In total, 267 patients had been randomised. Of those, 176 patients were treated with dabigatran etexilate and 90 patients according to SOC (1 randomised patient was not treated). 168 patients were 12 to less than 18 years old, 64 patients 2 to less than 12 years, and 35 patients were younger than 2 years.
Of the 267 randomised patients, 81 patients (45.8%) in the dabigatran etexilate group and 38 patients (42.2%) in the SOC group met the criteria for the composite primary endpoint (complete thrombus resolution, freedom from recurrent VTE, and freedom from mortality-related VTE). The corresponding rate difference demonstrated non-inferiority of dabigatran etexilate to SOC. Consistent results were also generally observed across subgroups: there were no significant differences in the treatment effect for the subgroups by age, sex, region, and presence of certain risk factors. For the 3 different age strata, the proportions of patients that met the primary efficacy endpoint in the dabigatran etexilate and SOC groups, respectively, were 13/22 (59.1%) and 7/13 (53.8%) for patients from birth to <2 years, 21/43 (48.8%) and 12/21 (57.1%) for patients aged 2 to <12 years, and 47/112 (42.0%) and 19/56 (33.9%) for patients aged 12 to <18 years.
Adjudicated major bleeds were reported for 4 patients (2.3%) in the dabigatran etexilate group and 2 patients (2.2%) in the SOC group. There was no statistically significant difference in the time to first major bleeding event. Thirty-eight patients (21.6%) in the dabigatran etexilate arm and 22 patients (24.4%) in the SOC arm had any adjudicated bleeding event, most of them categorised as minor. The combined endpoint of adjudicated major bleeding event (MBE) or clinically relevant non-major (CRNM) bleeding (on treatment) was reported for 6 (3.4%) patients in the dabigatran etexilate group and 3 (3.3%) patients in the SOC group.
An open label, single arm safety prospective cohort, multi-centre, phase III study (1160.108) was conducted to assess the safety of dabigatran etexilate for the prevention of recurrent VTE in paediatric patients from birth to less than 18 years. Patients who required further anticoagulation due to the presence of a clinical risk factor after completing the initial treatment for confirmed VTE (for at least 3 months) or after completing the DIVERSITY study were allowed to be included in the study.
Eligible patients received age and weight adjusted doses of an age-appropriate formulation (capsules, coated granules or oral solution) of dabigatran etexilate until the clinical risk factor resolved, or up to a maximum of 12 months. The primary endpoints of the study included the recurrence of VTE, major and minor bleeding events and the mortality (overall and related to thrombotic or thromboembolic events) at 6 and 12 months. Outcome events were adjudicated by an independent blinded adjudication committee.
Overall, 214 patients entered the study; among them 162 patients in age stratum 1 (from 12 to less than 18 years of age), 43 patients in age stratum 2 (from 2 to less than 12 years of age) and 9 patients in age stratum 3 (from birth to less than 2 years of age). During the on-treatment period, 3 patients (1.4%) had an adjudication-confirmed recurrent VTE within the first 12 months after treatment start. Adjudication-confirmed bleeding events during the on-treatment period were reported for 48 patients (22.5%) within the first 12 months. The majority of the bleeding events were minor. In 3 patients (1.4%), an adjudication-confirmed major bleeding event occurred within the first 12 months. For 3 patients (1.4%), adjudication-confirmed CRNM bleeding was reported within the first 12 months. No on-treatment deaths occurred. During the on-treatment period, 3 patients (1.4%) developed post-thrombotic syndrome (PTS) or had worsening of PTS within the first 12 months.