In this section : Haematology and Thrombosis
Myeloma
Warfarin
Anticoagulation for AF, DVT and PE
Orthopaedic VTE Risk Assessment
Haemolytic Anaemia
Platelet Transfusion
Parenteral Iron in Adults >18 Years
Pulmonary Embolism
Deep Vein Thrombosis of Lower Extremities
Bleeding with Other Antithrombotics
Low Molecular Weight Heparin
Haematinic Testing
Thromboprophylaxis for Non-Covid Patients
Thrombophilia Screening
Antithrombotics in Hip Fracture
Reversal of Warfarin
Lumbar Puncture, Antiplatelet & Anticoagulant Drugs
Antithrombotics & Surgery
Iron Deficiency Anaemia
Unfractionated Heparin Infusion
Massive Pulmonary Embolism
Warfarin
Last updated 30th June 2023
Introduction
- Warfarin is the preferred option for oral anticoagulation when DOACs are contra-indicated or not clinically appropriate.
- All patients on warfarin must be supplied with a yellow book, normally given by the pharmacy.
- Ensure patients are aware to ask for this book if you are not giving it at point of prescribing.
- The yellow book gives the patient important safety information, and space to record their INR and dosing schedule.
Target INR
- Treat to target INR, which varies according to indication:
- 2.5 ± 0.5 for most patients
- 3.0 ± 0.5 for some mechanical heart valves (always check with cardiology notes)
- Other targets may be advised by haematologists in specific circumstances
- Use treatment algorithms for dose initiation (for example, warfarin chart for hospital inpatients). Consider using a slow loading regime for anticoagulation in AF.
- Use LMWH for bridging (see below) whilst INR comes up to target levels.
Patient's Weight (kg) | Dose |
---|---|
<46 | 7,500 units daily |
46-56 | 10,000 units daily |
57-68 | 12,500 units daily |
69-82 | 15,000 units daily |
>82 | 18,000 units daily |
Drug Interactions
- Drug interactions are a key issue with warfarin and there have been several fatalities caused by drug interactions in this patient group.
- Be aware that not all medications causing INR increases are oral – for example, miconazole oral gel has been associated with fatal outcomes.
- Always check drug interactions before prescribing warfarin, or before prescribing any new medication for a patient already on warfarin.
- Individual drug interactions with warfarin are not listed here.
- Some foods also interact with warfarin. Patient information on this is in the yellow book. Patients are advised not to make significant changes to their diet without informing a prescriber.
Content by Alison Moore