Aspirin and an oral anticoagulant – can they be used together?

Apixaban, dabigatran and rivaroxaban (formerly known as NOACs^a) are non-vitamin K antagonist oral anticoagulants currently listed on the PBS.

Apixaban and rivaroxaban are selective inhibitors of factor Xa that block thrombin production, conversion of fibrinogen to fibrin, and thrombus development.¹ Dabigatran is a competitive and reversible direct thrombin inhibitor preventing thrombus formation.¹

Non-vitamin K antagonist oral anticoagulants are TGA registered and PBS listed for the prevention of stroke and systemic embolism in patients with non-valvular atrial fibrillation (NVAF) with one or more risk factors for stroke (Figure 1). Other indications include the prevention of venous thromboembolism, deep vein thrombosis and pulmonary embolism.^2,3

Apixaban, dabigatran and rivaroxaban have been shown to be as effective as warfarin in reducing the risk of stroke in patients with NVAF.⁴

Drug Utilisation Sub Committee (DUSC) data on PBS utilisation of apixaban, dabigatran and rivaroxaban show that use of warfarin has declined since the listing of these medicines on the PBS for NVAF.²

The analysis also reported that patients starting anticoagulant therapy for the first time are now more likely to start one of these three medicines than warfarin.²

Despite the growth in the use of apixaban, dabigatran and rivaroxaban, there are some concerns about their safety due to the risk of major bleeding (Figure 1).² As with other anticoagulants, clinical trials and post-market experience have shown major bleeding events, including those leading to death associated with apixaban, dabigatran and rivaroxaban.⁵

Figure 1. Non-vitamin K antagonist oral anticoagulant timeline for non-valvular atrial fibrillation.

Read the full report of the DUSC analysis on apixaban, dabigatran and rivaroxaban from the Department of Health.

As with any anticoagulants, safe and effective use of apixaban, dabigatran and rivaroxaban involves minimising the risk of thrombosis and bleeding.⁶ This involves carefully considering the suitability of one of these medicines for a particular indication, especially with regard to risk of bleeding, and the patient’s current stability on warfarin if switching from warfarin.⁷

Factors known to increase risk of bleeding

While the TGA stated that routine plasma monotoring is not required to manage bleeding in patients on one of these medicines,8 it is important to note that there are certain circumstances that may increase risk of bleeding.

The risk of bleeding is increased in patients who are on either apixaban, dabigatran or rivaroxaban and:^5,7,9

• are aged 75 years or over
• have special haemorrhagic risks from diseases or recent medical procedures
• have moderate renal impairment (creatinine clearance 30–50mL/min)
• have anaemia
• are concurrently taking NSAIDs and/or antiplatelets (eg, clopidogrel or low-dose aspirin).

Atrial fibrillation and coronary artery disease commonly occur together;¹⁰ thus patients are likely to be taking low-dose aspirin therapy in addition to an anticoagulant.

In patients with recent acute coronary syndrome, the addition of an anticoagulant to single antiplatelet therapy such as low-dose aspirin results in substantial increase in bleeding.¹¹

A recent meta-analysis showed that in patients receiving single low-dose aspirin, additional treatment with an oral anticoagulant decreased the rate of major adverse cardiovascular events by 30% but clinically significantly increased the rate of bleeding events by 79%.11

The Australian National Heart Foundation ACS guidelines recommend low-dose aspirin (100 mg–150 mg/day) be stopped in patients in whom an anticoagulant is indicated,¹² unless otherwise recommended by a cardiologist.

There have been reports of pharmacodynamic interactions between NSAIDs and this group of medicines that increase the risk of bleeding, as reflected in the pivotal trials of dabigatran¹³ and rivaroxaban.¹⁴

Despite this, unpublished data from the Australian Government Department of Veterans’ Affairs indicate that about 30% of veterans with atrial fibrillation taking aspirin, clopidogrel or warfarin monotherapy were co-prescribed concomitant NSAIDs or COX-2 inhibitors in 2012.⁹

More recent data from the Australian Government Department of Veterans’ Affairs indicate that NSAID use in 2013–14 was greater in patients taking apixaban, dabigatran or rivaroxaban compared with use in patients taking warfarin (8.7% vs 6.2%).⁴

These results are of concern, as they indicate that patients are taking an oral anticoagulant and an NSAID despite the increased risk of bleeding, particularly gastric bleeding.

Prescribers should carefully consider the concurrent use of non-vitamin K oral anticoagulant and NSAID and appropriately counsel their patients, as NSAIDs are easily accessible over the counter.

Other reasons that have contributed to bleeding incidents are:

• health professionals not recognising that apixaban, dabigatran and rivaroxaban are anticoagulants, thereby leading to concurrent prescribing of other anticoagulant medication
• inappropriate cessation of apixaban, dabigatran and rivaroxaban before surgical procedures.⁶

The NSW Clinical Excellence Commission NOAC Guidelines advise to use caution in the concomitant use of NSAIDs and apixaban, dabigatran or rivaroxaban, stating that antithrombotic interaction is similar to bleeding effects observed in antiplatelet and warfarin combinations.³

An antidote to reverse bleeding is now available for dabigatran. Idarucizumab (Praxbind) is TGA registered as:¹⁵

… a specific reversal agent for dabigatran and is indicated in patients treated with dabigatran etexilate (PRADAXA) when rapid reversal of the anticoagulant effects of dabigatran is required: – for emergency surgery / urgent procedures; – in life-threatening or uncontrolled bleeding.

Idarucizumab is available in hospitals and it not listed on the PBS. There are currently no antidotes for apixaban and rivaroxaban. 

• Advise patients to tell their doctor, dentist or pharmacist that they are taking an anticoagulant before starting or stopping any other medicine, herbal or over-the-counter products, particularly aspirin.
• Assess the need of aspirin in the patient’s management plan. Advise patients to avoid low-dose aspirin and other NSAIDs while taking an oral anticoagulant.
• Encourage patients to see a health professional if they have any unexplained bruising or bleeding, or pink, red or dark-brown urine.
• Recognise that there are treatment cessation protocols (Table 1) if they undergo any surgical procedures.
• If switching patients from warfarin to apixaban, dabigatran or rivaroxaban, warfarin should be stopped, INR measured daily and the new medicine started when the patient’s INR is < 2.5.³
• Report adverse events and major bleeding events to the TGA.