Anticoagulation 3: New oral anticoagulants

In Part 3 of our podcast series about anticoagulation, James talks to Dr Ed Abadir about the use of new oral anticoagulants, DOACs or NOACs, as alternatives to warfarin and heparin on the wards.

In Part 1 we discussed warfarin and in Part 2 we talked about heparin. To catch up on those podcasts, please visit Anticoagulation 1: Warfarin and Anticoagulation 2: Heparin.

Script Writer:  Laura Glenn

Editor:  James Edwards

Interviewee:  Ed Abadir

About Dr Ed Abadir

Edward Abadir is currently a Haematology registrar at Royal Prince Alfred Hospital and Concord Hospital. He studied medicine at the University of Sydney prior to internship and completed his residency at Royal Prince Alfred Hospital. Ed completed his Basic Physicians Training at Royal Prince Alfred Hospital in 2013.

Anticoagulation 3: New Oral Anticoagulants

With Dr Ed Abadir, Haematology registrar at Royal Prince Alfred Hospital & Concord Hospital, New South Wales, Australia.

Introduction

This podcast is about new oral anticoagulants, which are now commonly being used as alternatives to warfarin and heparin for both prophylactic and therapeutic anticoagulation.

  • DOACs (direct oral anticoagulants) are a group of new oral anticoagulant medications, which all directly inhibit the coagulation cascade. They are also known as NOACs (new/novel oral anticoagulants).
  • There are three DOACs currently listed on the PBS:
    • Apixaban
    • Rivaroxaban
    • Dabigatran
  • The most common indications in Australia for their use are:
    • Atrial fibrillation
    • DVT prophylaxis following orthopaedic surgery
    • Venous thromboembolism (DVT, PE) – n.b. only Rivaroxaban is licensed for this indication.

 

  • Mechanism of action
    • Dabigatran – direct thrombin inhibitor (inhibits factor II)
    • Apixaban&rivaroxaban – both factor Xa inhibitors
  • Half-lives
    • Their half-lives vary, but are especially dependent on renal function
      • All are contraindicated in patients with eGFR<30.
    • 8-15 hours is the standard half-life (patients with normal renal function).
  • Dosing interval
    • Apixaban&dabigatran – twice daily for therapeutic anticoagulation
    • Rivaroxaban
      • Initially twice daily for anticoagulation for DVT/PE, then becomes once daily.
      • Once daily for AF treatment
  • Drug-drug interactions (causing increased plasma levels of the DOAC)
    • Certain glycoprotein system inhibitors – mostly affect dabigatran
    • Cytochrome P450 inhibitorseg. -azole antifungals
  • They don’t need stringent monitoring.
  • They have a quicker onset of action than warfarin.
  • They have short half-lives, so their effect is discontinued quicker than warfarin when the drug is ceased.
  • No bridging therapy is required when a patient is commenced on a DOAC at the therapeutic dose.
  • The advantage over heparins is that they are orally administered.
  • It is difficult to judge the amount of anticoagulation a patient has on board at any time (because there is no quantitative test for the DOACs like the INR for monitoring warfarin, or the APTT for heparin).
    • Some coagulation tests can indicate whether the patient is likely to have a significant amount of anticoagulation on board or not (though they don’t accurately predict what the effect of the anticoagulation will be), for example:
      • Dabigatran – prolongs the thrombin time& the APTT
      • Rivaroxaban – increase the prothrombin time (PT)
      • Apixaban – more difficult, requires a modified anti-factor Xa level
    • Specific drug levels can be performed –if the drug level is undetectable, it is unlikely they have significant anticoagulation on board.
  • Unlike heparin & warfarin, there are no reversal agents.
  • If a patient on a DOAC has a life-threatening bleed, take the same steps as for any other patient:
    • Resuscitate as required, including volume replacement
    • Try to control the source
    • Correct other possible coagulopathies caused by the bleeding eg. consumption of platelets.
    • Consider the use of other blood products in consultation with a haematologist e.g. prothrombinex, activated factor VIIa or FEIBA (factor VIII inhibitor bypassing agent).
  • DOACs are new oral anticoagulants that are becoming more commonly used for treatment of patients with AF, DVT/PE and for VTE prophylaxis in patients who have undergone orthopaedic surgery.
  • The three agents currently on the PBS are dabigatran, apixaban and rivaroxaban.
  • Always check the patient’s renal function à all DOACs can accumulate in the context of renal impairment.
  • Ring for help EARLY if a patient on a DOAC has any significant bleeding.
  • For planned procedures & surgeries, it is important to plan ahead of time exactly when DOACs need to be stopped & re-started.
    • This will depend on local guidelines, the type of DOAC, the patient’s renal function & age.
    • 48-96 hours before surgery is usually a safe window (but depends on these factors!)

Related Podcasts

Tags: #anticoagulants,#anticoagulation,#apixaban,#bleeding,#dabigatran,#DOACs,#medication safety,#NOACs,#rivaroxaban

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