Key Points

• This document outlines the use of direct oral anticoagulants (DOACs) within their marketing authorisation and where clinically appropriate, in preference to warfarin (exceptions apply) for patients with atrial fibrillation who require anticoagulation.

• All patients newly initiated on anticoagulation should be referred to the anticoagulation team.

This is a controlled document. If you are using a printed copy, check it against the guidelines site to ensure you are using the latest edition. Print copies must be destroyed after use.

Abbreviations

AF	Atrial Fibrillation
BNF	British National Formulary
DOAC	Direct Oral Anticoagulants
CHA2DS2- VASc	Mnemonic standing for Congestive Heart Failure or left ventricular dysfunction, Hypertension, Age >75 years, Diabetes Mellitus, prior stroke, TIA or thromboembolism, Vascular disease, Age 65-74, Sex category
NG	Nasogastric
SPC	Summary of Product Characteristics

All patients new on anticoagulation should be referred to the Anticoagulant Clinic for initiation and review of treatment, unless counselling and all necessary information has been given to patient/carer by an appropriate health care professional.
Before initiation of any anticoagulant current weight and the following baseline bloods should be requested:
1. Full blood count (FBC)
2. Urea & Electrolytes (U&Es)
3. Liver function tests (LFTs)
4. Clotting screen & INR
Use the Cockcroft and Gault (C&G) formula to calculate renal function. The Cockcroft-Gault (C&G) equation is recommended by the manufacturers of all DOACs for calculating creatinine clearance (CrCl). eGFR should not be used.

Cockcroft and Gault equation for calculating CrCl

Creatinine Clearance CrCl = (140-age) X *Weight X 1.23(male)1.04(female)

                       Serum creatinine

                       (micromol/L)

*Use actual body weight kg

Anticoagulation is recommended in patients with AF with a CHA2DS2-VASc ≥1 for men or ≥2 for women. In practice, for patients with CHA2DS2-VASc score of 1, please consider individual risk factors on a case by case basis (see Appendix 1) Discuss with Cardiologist for advice when needed. Where a patient presents with a transient ischaemic Attack (TIA) or stroke, in the absence of alternative causes and where paroxysmal AF cannot be ruled out, anticoagulation to be considered.
All anticoagulants can cause significant bleeding risk. Before starting any anticoagulant careful consideration of bleeding risk should be undertaken. Tools such as the ORBIT Score (see Appendix 1) should be used to help quantify the bleeding risk.
When initiating warfarin refer to page 7&8.
If there is a clinical reason to switch anticoagulation, refer to Appendix 2.
If bridging is deemed clinically necessary, refer to section on Low molecular weight heparin and warfarin.

Weight (kg)	CrCl >20ml/min	CrCl 10-20ml/min	CrCl<10ml/min
<50	Dalteparin 2500 units s/c once daily	Dalteparin 2500 units s/c once daily	Unfractionated heparin 5000 units s/c twice daily
50-100	Dalteparin 5000 units s/c once daily	Dalteparin 2500 units s/c once daily
100-150	Dalteparin 5000 units s/c twice daily	Dalteparin 5000 units s/c once daily
>150	Dalteparin 7500 units s/c twice daily	Dalteparin 7500 units s/c once daily

Weight	Dose if CrCl > 20ml/min	Dose if CrCl < 20ml/min
< 46 kg	7500 units once daily	5000 units once daily
46-56 kg	10000 units once daily	6500* units once daily
57-68 kg	12500 units once daily	8500* units once daily
69-82 kg	15000 units once daily	10000 units once daily
83-98 kg	18000 units once daily	12500 units once daily
99-112 kg	10000 units twice daily	15000 units once daily
113-137 kg	12500 units twice daily	18000 units once daily
138-165 kg	15000 twice daily	10000 units twice daily
≥ 166 kg	18000 twice daily	12500 units twice daily

*Graduated syringes 10000 units in 1ml available for administration.

There is no need to routinely monitor anti-Xa assays in patients who weigh between 40- 180kg. Contact haematology for advice regarding monitoring.

For high-risk AF patients, consider warfarin loading doses, 10mg day 1, 10mg day 2, 5mg day 3 or 5mg daily. This requires daily INR monitoring.

For elderly patients, patients with a high risk of bleeding, and patients on interacting drugs, lower loading doses of warfarin are advised.

The following schedule (Fennerty et al 1984) should be used. Note that this requires daily INR tests.

U&E, including assessment of renal function	Repeat U & E’s annually if CrCl> 60ml/min. Repeat U & E’s every 6 months if CrCl 30-60ml/min Repeat U & E’s every 3 months if CrCl 15-30ml/min More frequent U & E’s advised if clinical status changes.
BP	Annually. More frequently if systolic close to or above 160mmHg.
FBC including Hb	Annually
Re-check stroke versus bleeding risk, i.e., CHA_2DS2VASc exceeds ORBIT bleed risk score	Annually, but more frequently if clinical status changes.
LFTs	Annually. More frequent LFT’s advised if inter current illness may impact hepatic function.
Weight	Annual

CHA2DS2-VASc criteria	Score	Tick if present
Congestive heart failure/ left ventricular dysfunction	1
Hypertension	1
Age >=75 yrs	2
Diabetes mellitus	1
Stroke/transient ischaemic attack/TE	2
Vascular disease (prior myocardial infarction, peripheral artery disease or aortic plaque)	1
Age 65–74 yrs	1
Sex category (i.e. female gender)	1
Score
If score ≥ 2 then indication for anticoagulation. If 1, consider it case by case

ORBIT			Score
Reduced Haemoglobin/Reduced Haematocrit/Anaemia Male Hb < 13g/dL or haematocrit < 40% Female Hb, 12g/dL or haematocrit < 36%			2
Age > 74 years			1
Bleeding Any history of GI bleeding, intracranial bleeding or haemorrhagic stroke			2
eGFR < 60ml/min/1.73m2			1
Treatment with antiplatelet agents			1
Score
Score	Risk Group	Bleeds per 100 patient years
0-2	Low	2.4
3	Medium	4.7
4-7	High	8.1

Drug	Switching from warfarin to DOAC	Switching from one DOAC to warfarin	Switching from one DOAC to another DOAC	Switching between a parenteral anticoagulant and a DOAC
Apixaban	Stop warfarin. Start Apixaban once INR < 2	Commence warfarin at normal initiation dose. Give apixaban and warfarin together for 2 days then check INR before next scheduled dose of apixaban. Dose warfarin as per INR. Continue concomitant treatment until INR ≥ 2.	The alternative DOAC can be initiated when the next dose is due. Patients must not be on more than one DOAC at any time.	Start new drug when dose of previous drug would have been due. Patients should not be on more than one drug at any time.
Dabigatran	Stop warfarin. Start Dabigatran once INR < 2	Adjust the starting time of the warfarin based on CrCL as follows: • CrCL ≥ 50ml/min start warfarin 3 days before discontinuing dabigatran • CrCL ≥ 30-< 50ml/min start warfarin 2 days before discontinuing dabigatran. Dabigatran can increase INR. The INR will better reflect effect of warfarin only after dabigatran has been stopped for at least 2 days. Until then, INR values should be interpreted with caution.
Rivaroxaban	Stop warfarin. Start Rivaroxaban as follows: -For prophylaxis of stroke and systemic embolism in nonvalvular AF: INR ≤ 3 -For patients treated for VTE and prevention of recurrence: ≤ 2.5	Commence warfarin at normal initiation dose. Give rivaroxaban and warfarin together for 2 days, then check INR immediately before next scheduled dose of rivaroxaban. Continue concomitant treatment until INR ≥ 2. There is a potential for inadequate anticoagulation during the transition from rivaroxaban to warfarin It should be noted that rivaroxaban can contribute to an elevated INR.
Edoxaban	Stop warfarin. Start Edoxaban once INR ≤ 2.5	Prior to starting warfarin, for patients on 60mg daily reduce dose to 30mg daily and for patients on 30mg daily reduce dose to 15mg daily edoxaban. Continue concomitant treatment until INR ≥ 2, for a maximum of 14 days. During combined therapy the INR should be checked a minimum of 3 times and immediately prior to the dose of edoxaban.

Version:	3.1
Guidelines Lead(s):	Harminder Sangha (Lead Anticoagulant Pharmacist) Preya Fakira (Lead Cardiology Pharmacist)
Contributor(s):	Tim Langran (Pharmacist- Associate Director of Medicines Optimisation – NHS Frimley)
Lead Director / Chief of Service:	Navin Chandra (WPH) & Sitara Khan (FPH) (Consultant Cardiologists – Clinical Leads)
Library check completed:	20/12/2024
Ratified at:	Cross site Cardiology Clinical Governance (3/9/24)
Date Issued:	10/09/2025
Review Date:	01/09/2027
Pharmaceutical dosing advice and formulary compliance checked by:	Alexandra Kirke August 2024
Key words:	Atrial fibrillation, Anticoagulation, DOAC, Edoxaban, Rivaroxaban, Apixaban, Dabigatran, Warfarin

This guideline has been registered with the Trust. However, clinical guidelines are guidelines only. The interpretation and application of clinical guidelines will remain the responsibility of the individual clinician. If in doubt, contact a senior colleague or expert. Caution is advised when using guidelines after the review date.

This guideline is for use in Frimley Health NHS Foundation Trust hospitals only. Any use outside this location will not be supported by the Trust and will be at the risk of the individual using it.

Version Control Sheet

Version	Date	Guideline Lead(s)	Status	Comment
1.0	May 2018	H Sangha, Lead Anticoagulant Pharmacist	Final
1.1	Oct 2022	H Sangha, Lead Anticoagulant Pharmacist	Draft	Scheduled review
2.0	May 2023	H Sangha, Lead Anticoagulant Pharmacist	Final
2.1	Nov 2023	H Sangha, Lead Anticoagulant Pharmacist	Interim	Replace reference to HAS-BLED score with ORBIT bleed risk score
3.0	September 2024	H Sangha, Lead Anticoagulant Pharmacist, P.Fakira, Lead Cardiology Pharmacist	Final	Changes to choice of DOAC
3.1	September 2025	H Sangha, Lead Anticoagulant Pharmacist, P.Fakira, Lead Cardiology Pharmacist	Interim	Anticoagulation for non-valvular atrial fibrillation (NVAF) section added LFT’s – ALT/AST >2 x ULN & Bilirubin > 1.5x ULN

Key Points

Introduction

Considerations when initiating anticoagulation

Cockcroft and Gault equation for calculating CrCl

Antiplatelets and anticoagulation

Low molecular weight heparin and warfarin

Prophylaxis Dose

Treatment Dose

Ongoing Monitoring Schedule by GP

References

Appendix 1: CHA2DS2-VASc and ORBIT scoring tool

Appendix 2: Switching between anticoagulant regimens

Appendix 3: DOAC Prescribing for Non-Valvular AF (NVAF)

Full version control record

Version Control Sheet