Anticoagulation Myth Busters

MYTH

“OAC should be avoided at the extremes of bodyweight”

REALITY

“Extremes of bodyweight not only impact on an individual’s cardiovascular risk, but can also influence the pharmacokinetics of antithrombotic medications, some of which may have a particularly narrow therapeutic window.

Whilst bodyweight and/or body mass index (BMI) can affect warfarin dosing requirements, their impact in clinical practice appears limited in view of the routine monitoring of INR and consequent dose adjustments required for maintenance of the desired therapeutic range.”1

There are limited data regarding the use of NOACs in patients with low bodyweight and their bleeding risk should always be carefully evaluated. Close clinical surveillance is recommended. Data to support the use of NOACs in obesity is also somewhat limited, recent guideline recommendations suggest that in those >120kg or with a BMI of ≥30 kg m−2 NOACs should be avoided due to concerns over underdosing.2 There may however, be some patients who are >120kg and were commenced on a NOAC before this guidance was published and may not want to switch to warfarin. In such patients, if there are concerns, it may be possible to request peak and trough plasma levels to ensure adequate levels of anticoagulation are achieved.3

General recommendations:1

Closer surveillance and more frequent monitoring and follow up may be required in underweight or obese patients.

Warfarin4

  • Little impact in view of routine monitoring and subsequent dose adjustments

NOACS
<50kg

  • Close clinical supervision (particularly if prescribed dabigatran)7

<60kg with one other risk factor

  • Apixaban – reduce dose from 5mg bd to 2.5mg bd6
  • Edoxaban – reduce dose from 60mg od to 30mg od7

>120kg or BMI >40kg/m2

  • NOACs are not recommend – consider warfarin in preference2,3
REFERENCES
  1. Rocca B, Fox KAA, Ajjan RA, Andreotti F, Baigent C, Collet JP, et al. Antithrombotic therapy and body mass: an expert position paper of the ESC Working Group on Thrombosis. European Heart Journal. 2018.
  2. Martin K, Beyer-Westendorf J, Davidson BL, Huisman MV, Sandset PM, Moll S. Use of the direct oral anticoagulants in obese patients: guidance from the SSC of the ISTH. Journal of thrombosis and haemostasis : JTH. 2016;14(6):1308-13.
  3. Steffel J, Verhamme P, Potpara TS, Albaladejo P, Antz M, Desteghe L, et al. The 2018 European Heart Rhythm Association Practical Guide on the use of non-vitamin K antagonist oral anticoagulants in patients with atrial fibrillation: executive summary. Europace. 2018.
  4. SmPC Warfarin. medicines.org.uk: medicines.org.uk; 2019.
  5. SmPC Dabigatran. medicines.org.uk; 2019.
  6. SmPC Apixaban. medicines.org.uk: medicines.org.uk; 2019.
  7. SmPC Edoxaban. medicines.org.uk: medicines.org.uk; 2019.
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