Dabigatran (Pradaxa) for stroke prevention in patients with non-valvular atrial fibrillation

• Dabigatran is an oral anticoagulant
  It is a direct thrombin inhibitor.
• Dose titration and monitoring of prothrombin time are not required
  Dabigatran is formulated as a capsule (150 mg or 110 mg) taken twice daily.
• Dabigatran 150 mg twice daily reduced the absolute risk of stroke or systemic embolism by 0.6% per year compared with warfarin
  The incidence of stroke or systemic embolism did not differ between dabigatran 110 mg twice daily and warfarin.
• Important differences in effectiveness were related to the quality of INR control in clinical trial patients
  Consistently therapeutic warfarin may be as effective as dabigatran.
• The overall rate of major bleeding did not differ between dabigatran 150 mg twice daily and warfarin
  Dabigatran 150 mg twice daily increased the risk of gastrointestinal bleeding, but reduced the risk of intracranial bleeding.
• There is no antidote to dabigatran-induced bleeding
  As with all anticoagulants, tell patients to seek prompt medical attention for unexplained bruising, blood in the urine or black stools.
• Dabigatran is contraindicated in severe hepatic and renal impairment (creatinine clearance ≤ 30 mL/min)
  Consider dabigatran 110 mg twice daily in patients with moderate renal impairment (creatinine clearance 30–50 mL/min).

Dabigatran is PBS listed for the prevention of stroke or systemic embolism in moderate-to-high risk patients with non-valvular atrial fibrillation who meet certain criteria outlined in the listing restriction.

Dabigatran is a direct thrombin (factor IIa) inhibitor oral anticoagulant. It is formulated as dabigatran etexilate, a prodrug converted to dabigatran after administration.

For information about dabigatran's pharmacokinetic profile, read the Australian Prescriber article: New oral anticoagulant drugs — mechanisms of action.

From 1 September 2013 dabigatran is PBS listed for preventing stroke and systemic embolism in patients with non-valvular atrial fibrillation and at least one additional risk factor for stroke.² Both the indication and patient population are consistent with those evaluated in the main clinical trial (see How does it compare?).

In April 2010, dabigatran was PBS listed for the prevention of venous thromboembolism after orthopaedic surgery. Dabigatran (150 mg once daily or 220 mg once daily) is taken for 10 days after knee replacement surgery and for 28–35 days after hip replacement surgery. For further information refer to the NPS RADAR review Dabigatran (Pradaxa) for preventing venous thromboembolism after hip or knee replacement surgery.

Review current anticoagulant control when considering dabigatran for patients with atrial fibrillation

Warfarin-treated patients with unstable or poor INR control (for reasons other than non-adherence) may benefit if switched to dabigatran. Factors that contribute to the suboptimal use of warfarin, including drug interactions and difficulty monitoring INR, may also inform the decision to switch therapy.

Patients with consistently therapeutic INRs while taking warfarin, who are at low risk of stroke, may be less likely to benefit from a switch to dabigatran. Some of these patients may also find frequent anticoagulant monitoring reassuring.

Consider dabigatran for patients who are unwilling to take warfarin because of drug interactions, dietary restrictions or the need for regular monitoring.asure of the risk of stroke in which congesti

Dabigatran may be unsuitable for patients with serious comorbidities

There are likely to be important differences between the dabigatran clinical trial population and patients treated in the community. For example, severe renal impairment (CrCl ≤ 30 mL/min) was among the exclusion criteria³, and warfarin should therefore continue to be the preferred drug for this patient population.

Patients with conditions associated with an increased risk of bleeding (Box 1) or active liver disease were also ineligible and should not receive dabigatran.

Clinical trial investigators excluded patients thought unlikely to adhere to dosing instructions.³ If patient adherence is an issue in clinical practice, the longer terminal half-life of warfarin is likely to provide a more consistent anticoagulant effect. Furthermore, prothrombin time cannot be used to guide management or monitor adherence in dabigatran-treated patients.

• Major surgery in the previous month
• Planned surgery or intervention in the next 3 months
• History of intracranial, intraocular, spinal, retroperitoneal or atraumatic intra-articular bleeding
• Gastrointestinal haemorrhage within the past year
• Symptomatic or endoscopically documented gastroduodenal ulcer disease in the previous 30 days
• Haemorrhagic disorder or bleeding diathesis
• Need for anticoagulant treatment of disorders other than atrial fibrillation
• Fibrinolytic agents within 48 hours of study entry
• Uncontrolled hypertension (systolic blood pressure > 180 mmHg and/or diastolic blood pressure > 100 mmHg)
• Recent malignancy or radiation therapy (≤ 6 months) and not expected to survive for 3 years

The absolute risk of stroke and risk of major bleeding guide the choice of antithrombotic therapy in patients with non-valvular atrial fibrillation (see NPS News 62: Using antithrombotics wisely in stroke prevention).

Patients at moderate to high risk of stroke are currently prescribed warfarin. It reduces the relative risk of stroke in non-valvular atrial fibrillation by 64% compared with placebo or no treatment.⁴

Fixed-dose dabigatran is an alternative to warfarin for the primary and secondary prevention of stroke.

Before prescribing dabigatran consider that:

• patients with an INR consistently in the therapeutic range may not benefit from switching therapy (see Who is it for?)
• safety has not been established in patients at high risk of bleeding (Box 1)
• renal impairment increases bleeding risk.

Dabigatran has been compared with warfarin in patients with non-valvular atrial fibrillation and at least one additional risk factor for stroke.⁵ The RE-LY study randomised more than 18,000 patients at risk of stroke (mean CHADS2* score 2.1) to dabigatran 150 mg twice daily, dabigatran 110 mg twice daily or dose-adjusted warfarin.^3,5 The dabigatran dose was blinded whereas warfarin was administered in an open-label fashion. To minimise bias, outcomes were adjudicated by investigators blinded to treatment assignment. The mean age of study participants was 71 years and the median follow-up period was 2 years. Half the patients enrolled in the RE-LY study were naïve to oral anticoagulants.

Dabigatran reduces stroke and systemic embolism

Dabigatran 150 mg twice daily reduced risk more than dabigatran 110 mg twice daily.^5,6 The higher dabigatran dose reduced the annual absolute risk of stroke or systemic embolism by 0.6% compared with warfarin (RR 0.65, 95% CI 0.52 to 0.81) and by 0.43% compared with dabigatran 110 mg twice daily (Table 1). Both haemorrhagic and ischaemic stroke occurred less often in the dabigatran 150 mg twice-daily group than in the warfarin group.

Dabigatran 110 mg twice daily was non-inferior to warfarin. That is, a similar number of patients in each treatment group had a stroke or systemic embolism. Compared with warfarin, dabigatran significantly reduced the incidence of haemorrhagic, but not ischaemic, stroke.

Table 1.
Annual incidence of study outcomes in the RE-LY trial^5,6

* Primary study outcome

† Includes haemorrhagic, ischaemic or unspecified, non-disabling and disabling or fatal stroke

‡ p < 0.05. All values are for superiority over warfarin

Warfarin-treated patients with an INR consistently in the therapeutic range may not benefit from switching to dabigatran

The INR in the warfarin group was within the therapeutic range (2.0–3.0) for 64% of the RE-LY study period, but the quality of INR control varied between countries and study sites.5,7

Study centres in Australia reported a mean time in therapeutic range of 74 %; a figure within the upper quartile (top 25%) of participating study sites.7 Post-hoc analyses found that dabigatran 150 mg twice daily reduced the rate of composite cardiovascular events† at centres where INR control was poor (bottom 25%), but not at sites where INR control was better (Figure 1). Patients with an INR consistently in the therapeutic range may therefore be less likely to experience a net clinical benefit† by switching to dabigatran therapy.

† The RE-LY study specified a composite net clinical benefit outcome of stroke, systemic embolism, pulmonary embolism, myocardial infarction, death and major bleeding.

Serious bleeding is the greatest safety concern for dabigatran-treated patients and clinicians. However, unlike for warfarin, there is currently no specific antidote to dabigatran's effect.

Rates of discontinuation were significantly higher in dabigatran- than warfarin-treated patients in the RE-LY study (21% vs 17%, respectively); gastrointestinal (GI) disorders were the most common adverse effect leading to discontinuation of dabigatran (see Gastrointestinal disorders may affect adherence).^5,8

Report suspected adverse reactions to the Therapeutic Goods Administration (TGA) online or by using the 'Blue Card' distributed three times a year with Australian Prescriber. For information about reporting adverse reactions, see the TGA website.

Major bleeding rate did not differ between dabigatran 150 mg twice daily and warfarin

Patients at risk of bleeding were excluded from the RE-LY study (Box 1).³

Major bleeding rates were similar for dabigatran 150 mg twice daily and warfarin (RR 0.93, 95% CI 0.81 to 1.07) in the total study population (Table 2).^5,6 However, the incidence of major bleeding was lower with dabigatran 110 mg twice daily than with warfarin (0.7% per year; RR 0.8, 95% CI 0.7 to 0.93).

Warfarin was associated with a higher rate of life-threatening bleeds than either dabigatran dose.

Table 2.
Annual incidence of major and life-threatening bleeding in the RE-LY trial^5,6

* Defined as a reduction in the haemoglobin level of at least 20 g/L, transfusion of at least two units of blood, or symptomatic bleeding in a critical area or organ

† A subcategory of major bleeding consisting of fatal bleeding, symptomatic intracranial bleeding, bleeding with a decrease in the haemoglobin level of at least 50 g/L, or bleeding requiring transfusion of at least four units of blood or inotropic agents or necessitating surgery

‡ p < 0.05. All values are for superiority over warfarin

Poor INR control was associated with increased bleeding risk

Post-hoc analyses of RE-LY data suggest that there are differences in bleeding risk between dabigatran and warfarin when the quality of INR control is poor.7

At study centres where INR control was poor, dabigatran 150 mg twice daily reduced the incidence of major bleeding compared with warfarin (Figure 2). However, there was no significant difference in risk with better INR control (mean time in therapeutic range ≥ 57.1%).

More dabigatran-treated patients had a gastrointestinal bleed

Compared with warfarin, the rate of major GI bleeding (Table 3) was significantly higher in patients treated with dabigatran 150 mg twice daily (RR 1.47; 95% CI 1.17 to 1.85).² The risk increased with age and was greatest in patients aged ≥ 75 years (hazard ratio [HR] 1.79, 95% CI 1.32 to 2.42).⁸

Dabigatran 150 mg twice daily caused significantly more major GI bleeds than warfarin at study centres where INR control was above the median (mean time in therapeutic range > 65.5%).⁷

Table 3.
Annual incidence of GI bleeding in the RE-LY trial²

* A subset of major bleeding

† Significantly greater incidence of gastrointestinal bleeding compared with warfarin (p < 0.05)

Intracranial bleeding was uncommon, but higher with warfarin

Dabigatran 150 mg twice daily reduced the absolute risk of intracranial bleeding compared with warfarin (0.32 % vs 0.76 %, respectively; RR 0.41, 95% CI 0.28 to 0.6).

Gastrointestinal disorders may affect adherence

Gastrointestinal adverse events, including dyspepsia and gastritis-like symptoms, were common in dabigatran-treated patients (35% vs 24% in the warfarin group).² In the RE-LY study, gastrointestinal disorders frequently led to drug discontinuation (7%, 6.5% and 3.9% in the dabigatran 150 mg twice-daily, dabigatran 110 mg twice-daily and warfarin groups, respectively).⁸

There is no antidote to dabigatran-induced bleeding

Stopping dabigatran may be sufficient to manage minor bleeding in patients with normal renal function because dabigatran binds reversibly to thrombin and has a relatively short mean terminal half-life (12–14 hours).^2,9 The Pradaxa (dabigatran) product information suggests supportive strategies, including transfusion of fresh whole blood or fresh frozen plasma, for severe bleeding.²

Take care combining dabigatran with antiplatelet drugs or NSAIDs

Combining dabigatran with other anticoagulants or antiplatelet agents, including clopidogrel, is not recommended.² Seek expert advice for patients with an indication for ongoing antiplatelet therapy.

Patients in the RE-LY study were permitted to take concomitant aspirin (< 100 mg/day) and/or clopidogrel.⁵ Each drug, or the combination thereof, contributed to an increase in the annual rate of major bleeding events.^2,8

NSAIDs increased the relative risk of major bleeding by up to 50% when given in conjunction with dabigatran or warfarin.²

Dabigatran has a different drug interaction profile to that of warfarin

Use dabigatran cautiously in patients taking amiodarone, HIV-protease inhibitors or verapamil. These and other inhibitors of P-glycoprotein can increase dabigatran plasma levels and, therefore, the risk of bleeding.

Starting dabigatran and verapamil simultaneously is contraindicated.² Verapamil can be added to dabigatran therapy, but dabigatran must be given 2 hours before verapamil^‡ to avoid interaction. Consider other treatment options for patients unlikely to be able to comply with these dosing instructions.

The strong P-glycoprotein inhibitors cyclosporin, tacrolimus and itraconazole are not recommended in patients taking dabigatran; systemic ketoconazole is contraindicated.²

An increased risk of myocardial infarction cannot be excluded

Myocardial infarction occurred at a numerically, but not statistically significantly, greater rate in dabigatran- than warfarin-treated patients (annual event rate in the RE-LY study: dabigatran 150 mg twice daily: 0.81%; dabigatran 110 mg twice daily 0.82%; warfarin 0.64%).^5,6 The imbalance did not appear to be related to dabigatran dose.^5,10

Avoid dabigatran in patients with hepatic impairment

Dabigatran should not be used by patients with liver disease or severe hepatic impairment expected to impact on survival.² Active liver disease, elevated liver enzyme levels at baseline (more than twice the upper limit of normal) or after previous exposure to ximelagatran^§ were exclusion criteria in the RE-LY study.^3,5

The Pradaxa product information recommends that each patient has a liver function test before beginning treatment with dabigatran.²

Dabigatran caused similar rates of elevated liver enzyme levels to those seen with warfarin in the RE-LY study.⁵

The recommended dose of dabigatran is 150 mg twice daily, taken with or without food. The capsule should be swallowed whole with water. Breaking, chewing or emptying the contents increases the dose absorbed and the risk of bleeding.²

Reduce the dose to 110 mg twice daily for patients aged ≥ 75 years. Consider prescribing the lower dose for patients with moderate renal impairment (CrCl 30–50mL/min) or those at higher risk of major bleeding.

Dabigatran is contraindicated in patients:^¦

• with severe renal impairment (CrCl < 30 mL/min)
• predisposed to bleeding
• with conditions associated with an increased risk of bleeding (Box 1)
• with GI haemorrhage within the last year
• with liver disease or hepatic impairment expected to impact on survival.

Switching patients from warfarin to dabigatran

Stop warfarin and wait until the patient's INR is < 2.0 before starting dabigatran.²

Switching patients from dabigatran to warfarin

Use CrCl to determine when warfarin should be started. For patients with CrCl:

• > 50 mL/min, start warfarin 3 days before stopping dabigatran
• 31–50 mL/min, start warfarin two days before stopping dabigatran.

Discontinue dabigatran before surgery

Dabigatran should be stopped at least 1 day (CrCl ≥ 50mL/min) or 3 days (CrCl < 50mL/min) before elective surgery or an invasive procedure.^2,13

Discontinue dabigatran 2–4 days before surgery if complete haemostasis is required.

Store dabigatran in its original packaging

Dabigatran capsules should be dispensed and stored in the manufacturer's original packaging.^14,15 Repackaging dabigatran capsules increases the risk of exposure to moisture or humidity, causing product breakdown and loss of potency.

Patients and their carers should clearly understand the risks and potential benefits of taking an anticoagulant to prevent stroke. Refer to NPS News 62: Using antithrombotics wisely in stroke prevention for a discussion of effective risk communication.

Advise patients and carers:^14–16

Discuss the Pradaxa Consumer Medicine Information (CMI) leaflet with the patient.

Medicine Update

An NPS Medicine Update article on dabigatran for preventing stroke is available for consumers. Medicine Update helps consumers to ask the right questions about new medicines, and helps them compare the potential benefits and harms of a new medicine with those of other medicines.