Anticoagulation choice and duration

01Purpose and principlesWhat the treatment does and how it fits into care.

Anticoagulation is a risk-exchange rather than a generic response to a raised clot risk. The benefit depends on the untreated probability and consequence of thrombosis; harm depends on active bleeding, anatomy, renal and hepatic clearance, interacting medicines, frailty and the feasibility of correct dosing. Confirm that the proposed dose is for acute treatment, extended prevention, atrial fibrillation or surgical prophylaxis. These are not interchangeable. Establish baseline FBC, renal and liver function, weight, blood pressure, pregnancy potential, bleeding history, current antiplatelets and the clinical indication before the first dose.

In acute DVT or PE, apixaban and rivaroxaban can be started orally with intensified initial regimens. Dabigatran or edoxaban follows at least 5 days of therapeutic LMWH or UFH. If a DOAC is unsuitable, NICE supports LMWH followed by dabigatran or edoxaban, or LMWH/UFH with a vitamin K antagonist until the INR is therapeutic. Choice must account for severe renal impairment, extremes of weight, malabsorption or gastrointestinal surgery, cancer site, pregnancy, breastfeeding, antiphospholipid antibodies, adherence and CYP3A4 or P-glycoprotein interactions.

Duration follows the clot story. Treat proximal DVT or PE for at least 3 months, and active cancer-associated VTE for 3 to 6 months before reassessing. A major transient factor such as recent surgery that has resolved favours stopping after 3 months if the course was uncomplicated. Unprovoked VTE, recurrence, persistent inflammatory or malignant risk and some high-risk thrombophilias increase recurrence after stopping. Male sex, proximal clot and elevated post-treatment D-dimer can inform but do not replace shared clinical assessment. Distal DVT, unusual-site thrombosis and superficial thrombophlebitis require their own pathways rather than automatic extrapolation.

For atrial fibrillation, NICE uses CHA2DS2-VASc to estimate embolic risk and recommends a DOAC for most eligible adults, considering anticoagulation in men with a score of 1 and offering it at 2 or more. Review bleeding risks with ORBIT and correct them, but do not assume sinus rhythm after ablation removes stroke risk. Mechanical valves require a vitamin K antagonist with a valve-specific INR target. Bioprosthetic valves, mitral stenosis and recent coronary stenting need cardiology-led interpretation because the valve type, rhythm and antiplatelet period change therapy.

Long-term treatment remains an active prescription. Review at least annually, and sooner after acute kidney injury, weight change, bleeding, falls, new cancer therapy or interacting medicine. Check whether the original indication remains, whether the dose still matches renal function and age or weight criteria, and whether adherence is reliable. Explain signs of bleeding and thrombosis, safe analgesia, alcohol moderation, pregnancy planning, travel and the need to disclose treatment before procedures. A documented stop or review date prevents both avoidable recurrence and accidental indefinite exposure.

Key points

Define the indication before the drug: venous thromboembolism, atrial fibrillation, mechanical valve, acute coronary disease and thromboprophylaxis use different agents, doses and endpoints.
For confirmed proximal DVT or PE, NICE recommends at least 3 months of anticoagulation; review at 3 months whether the event was provoked, unprovoked, cancer associated or still supported by a persistent risk.
Apixaban or rivaroxaban is a first-line option for most adults with DVT or PE when renal function, interactions, body context, adherence and bleeding risk permit.
Dabigatran and edoxaban require at least 5 days of therapeutic parenteral anticoagulation before their VTE treatment phase; apixaban and rivaroxaban use an oral loading phase instead.
Use a vitamin K antagonist rather than a DOAC for a mechanical prosthetic valve; warfarin is also generally preferred for thrombotic antiphospholipid syndrome, especially triple-positive disease.
Calculate creatinine clearance with Cockcroft–Gault for DOAC dosing: an automatically reported eGFR can overestimate function in older, low-weight or acutely unwell adults.
A transient provoking factor that has resolved usually supports stopping after the treatment course; unprovoked or persistent-risk VTE requires an explicit recurrence-versus-bleeding discussion and at least annual review if continued.
Do not use a bleeding score as the sole reason to withhold indicated anticoagulation; identify modifiable hazards such as uncontrolled hypertension, interacting antiplatelets, alcohol excess and untreated bleeding lesions.
Record the exact medicine, indication, dose, renal calculation, intended duration, review date, missed-dose advice and peri-procedural contact route at every transition of care.

02Indications, selection and cautionsWho may benefit, who needs urgent treatment and important alternatives.

Indication and phase

Identify acute treatment, secondary prevention, atrial fibrillation, valve disease or prophylaxis; each has a different evidence-based dose and duration.

Recurrence context

Separate a resolved major transient trigger from unprovoked, recurrent, cancer-associated or persistent-risk thrombosis because recurrence after withdrawal differs substantially.

Bleeding phenotype

Ask about previous intracranial or gastrointestinal bleeding, anaemia, renal failure, liver disease, uncontrolled blood pressure, falls, alcohol and concurrent antiplatelets or NSAIDs.

Drug-selection modifiers

Mechanical valves, triple-positive APS, pregnancy, breastfeeding, cancer site, severe kidney disease, malabsorption, adherence and interacting drugs can displace a usual DOAC choice.

Patient priorities

Explore once- versus twice-daily dosing, monitoring tolerance, reversibility concerns, work and travel, pregnancy plans and preference after quantified risks are discussed.

Red flags requiring action

Haemodynamic instability, syncope, severe hypoxaemia or right-heart strain with suspected PE requires an emergency reperfusion assessment rather than an ordinary outpatient anticoagulation decision.
Head injury, new focal neurology, severe headache, gastrointestinal haemorrhage, haemodynamic compromise or a rapid haemoglobin fall while anticoagulated requires urgent bleeding assessment and source control.
Pregnancy, a mechanical valve, severe renal failure, active cancer, antiphospholipid syndrome, thrombocytopenia or suspected heparin-induced thrombocytopenia changes the usual drug pathway and needs specialist input.

03Assessment before treatmentTests and checks that guide safe selection.

Investigation order

Read from the initial assessment onwards. Tests may run in parallel in urgent care; first-line, preferred, confirmatory, definitive and gold-standard labels appear only when the chapter explicitly states them.

01
First-line: FBC, renal, liver and weight assessmentFirst stepFirst line
Why
Establish bleeding reserve and calculate a safe agent-specific dose.
Interpretation and limitations
Use current actual weight and Cockcroft–Gault creatinine clearance for DOAC decisions. Thrombocytopenia, unexplained anaemia, acute kidney injury or significant hepatic coagulopathy requires cause assessment before routine prescribing.
02
Indication-specific confirmation
Why
Avoid exposing a patient to anticoagulation for an unconfirmed or incorrectly classified event.
Interpretation and limitations
Use the relevant objective pathway: compression ultrasound for DVT, CT pulmonary angiography or V/Q imaging for PE, ECG documentation for AF and operative or echocardiographic records for valve type.
03
Interaction and adherence review
Why
Identify reduced efficacy, accumulated exposure or a regimen the patient cannot take reliably.
Interpretation and limitations
Check strong P-glycoprotein and CYP3A4 inhibitors or inducers, antiplatelets, NSAIDs, SSRIs, herbal products and missed doses; use a pharmacist when combinations are complex.
04
Selective antiphospholipid testingPreferred
Why
Detect a condition that can change the preferred long-term anticoagulant.
Interpretation and limitations
Test only when the clinical context would change management and interpret lupus anticoagulant carefully during anticoagulation. Persistence at least 12 weeks apart is required for APS classification.
05
Selective bleeding-source assessment
Why
Correct a modifiable lesion rather than simply reducing an indicated dose.
Interpretation and limitations
Investigate iron deficiency, haematuria, recurrent epistaxis, abnormal uterine bleeding or gastrointestinal symptoms using the appropriate pathway; do not label occult malignancy as a medicine side effect.

04Treatment approachPreparation, options, escalation and aftercare.

01Confirmed acute VTESelect and start treatmentFirst stepObjective imaging confirms proximal DVT or PE and there is no immediate reperfusion indication.

1Assess haemodynamics, bleeding, renal and liver function, weight, pregnancy, cancer, APS and interactions.
2Use apixaban or rivaroxaban when suitable, or give therapeutic heparin before dabigatran, edoxaban or a vitamin K antagonist pathway.
3Give written dose-phase instructions and set a 3-month review before discharge or handover.

02Three-month VTE reviewDecide stop or extendThe minimum course is complete and acute symptoms have stabilised.

1Reconstruct whether the event was provoked by a resolved factor, unprovoked, recurrent, cancer associated or driven by a persistent risk.
2Compare recurrence consequence with bleeding risk, patient preference and the feasibility of a licensed extended-dose regimen.
3Stop with safety-netting or continue with a named dose and at least annual review; document the rationale rather than writing lifelong without reassessment.

03Atrial fibrillationPrevent cardioembolic strokeClinical AF is documented and stroke-prevention assessment is required.

1Calculate CHA2DS2-VASc and review bleeding risk using ORBIT while correcting reversible hazards.
2Offer an appropriately dosed DOAC to most eligible adults, or use a vitamin K antagonist when a DOAC is unsuitable or valve pathology requires it.
3Review renal function, adherence, bleeding and continued indication at least annually and after major clinical change.

04Special populationMove to an expert pathwayMechanical valve, pregnancy, APS, severe organ failure, cancer-associated thrombocytopenia or unusual-site thrombosis is present.

1Do not extrapolate a routine DOAC regimen to an excluded or high-risk group.
2Stabilise acute thrombosis or bleeding and gather valve, pregnancy, platelet, renal, liver, cancer and interaction details.
3Agree agent, intensity, monitoring and duration with the appropriate haematology, cardiology, obstetric, renal or cancer team.

05Regimens, contraindications and interactionsTreatment details and the circumstances that modify them.

A first-line oral option for most adults with confirmed DVT or PE and a common stroke-prevention option in non-valvular atrial fibrillation.

Apixaban

For acute DVT or PE give 10 mg orally twice daily for 7 days, then 5 mg twice daily; after 6 months, 2.5 mg twice daily may be used for extended prevention when continued treatment is chosen.

Use the indication-specific SmPC renal criteria; do not apply AF dose-reduction rules to acute VTE. Avoid active major bleeding and strong dual CYP3A4/P-gp interactions, review severe renal or hepatic impairment, and avoid during pregnancy or breastfeeding.

A single-drug first-line VTE pathway that avoids initial heparin when suitable and is also licensed for stroke prevention in non-valvular atrial fibrillation.

Rivaroxaban

For acute DVT or PE give 15 mg orally twice daily with food for 21 days, then 20 mg once daily with food; after at least 6 months, 10 mg once daily is an extended-prevention option, with 20 mg considered when recurrence risk is high.

The 15 mg and 20 mg tablets must be taken with food. Use Cockcroft–Gault renal assessment, avoid CrCl below 15 mL/min, active bleeding and strong combined CYP3A4/P-gp inhibitors, and assess gastrointestinal bleeding, liver disease, pregnancy and adherence.

A direct thrombin inhibitor with a specific reversal agent, used for VTE and eligible atrial fibrillation when renal function and gastrointestinal tolerance are suitable.

Dabigatran etexilate

For DVT or PE give 150 mg orally twice daily after at least 5 days of therapeutic parenteral anticoagulation; use the licensed 110 mg twice-daily reduction when age, interacting verapamil or an individual bleeding assessment meets SmPC criteria.

Renal clearance is substantial: calculate Cockcroft–Gault CrCl and avoid VTE treatment below 30 mL/min. Swallow capsules whole, review dyspepsia, P-gp interactions and age-related bleeding, and avoid mechanical valves, pregnancy and breastfeeding.

A once-daily factor Xa inhibitor for VTE after heparin lead-in and for eligible non-valvular atrial fibrillation.

Edoxaban

For DVT or PE give 60 mg orally once daily after at least 5 days of therapeutic parenteral anticoagulation; reduce to 30 mg once daily for CrCl 15–50 mL/min, body weight 60 kg or less, or specified P-gp inhibitors.

Use Cockcroft–Gault, avoid CrCl below 15 mL/min and review very high renal clearance for AF efficacy according to the SmPC. Avoid active bleeding, mechanical valves, pregnancy and breastfeeding and assess hepatic disease and interactions.

Preferred for mechanical prosthetic valves and generally for thrombotic APS, and an alternative when DOAC treatment is unsuitable or monitoring is desired.

Warfarin

Start with a locally validated loading schedule and adjust the daily oral dose to the indication-specific INR; a common target is INR 2.5 with therapeutic range 2.0–3.0, while mechanical valves require valve-specific targets.

Bridge acute VTE with therapeutic heparin for at least 5 days and until INR is therapeutic for the locally required interval. Review interacting medicines, diet, alcohol and adherence; warfarin is teratogenic and pregnancy management requires a specialist valve or thrombosis plan.

06Complications, monitoring and follow-upAdverse effects, response and longer-term review.

Before treatment document FBC, weight, Cockcroft–Gault creatinine clearance, liver tests, blood pressure, bleeding and thrombotic history, interacting medicines and pregnancy status where relevant.
For a DOAC, review at least annually and more often when older, frail or renally impaired; an often-used maximum interval in months is approximately CrCl divided by 10, with immediate reassessment during acute illness.
For warfarin, use INR frequency determined by stability and recent changes; check sooner after an interacting medicine, acute illness, diet or alcohol change, missed doses or unexplained bleeding.
At every review verify the indication, correct dose and phase, adherence, bleeding, anaemia, renal change, falls, planned procedures and whether concurrent antiplatelet or NSAID therapy remains necessary.
If extended anticoagulation continues after VTE, review the recurrence and bleeding balance at least annually and record why full-dose, reduced-dose or withdrawal remains appropriate.

07Special situationsVariants, exceptions and circumstances that change the usual approach.

Phase errors cause harm

The most dangerous prescribing errors are often correct drugs at the wrong phase: omitted DOAC loading, failure to reduce after loading, or inappropriate low-dose secondary prevention during an acute recurrence.

Renal estimate matters

DOAC trials and product dosing use Cockcroft–Gault creatinine clearance. Laboratory eGFR is indexed and can misclassify small, older or rapidly changing patients.

Provoked needs precision

Calling every immobilised patient provoked obscures recurrence risk. Record the strength, timing and resolution of surgery, trauma, pregnancy, hormone exposure, illness or persistent disease.

Patient preference is clinical

A medicine that is unaffordable, intolerable, difficult to swallow or repeatedly missed does not deliver trial efficacy; regimen fit belongs in the risk assessment.

Scores support decisions

CHA2DS2-VASc and ORBIT structure AF review, but they do not replace examination of active bleeding, frailty, prognosis, renal trajectory and correctable hazards.

08Common pitfallsFrequent interpretation and management errors.

01
Do not reduce a DOAC empirically because a patient looks frail; use the licensed indication-specific criteria, because underdosing can preserve bleeding risk while losing thrombosis protection.
02
Do not prescribe a DOAC for a mechanical prosthetic valve or assume all valve disease is equivalent; establish the valve type, position and target with cardiology records.
03
Do not order indiscriminate thrombophilia testing during acute thrombosis or anticoagulation; results can be distorted and rarely alter the immediate treatment course.
04
Do not stop at 3 months solely because the calendar has elapsed; first classify the trigger, persistent risks, recurrence history and bleeding burden with the patient.
05
Do not continue aspirin or clopidogrel by inertia when anticoagulation starts; identify the coronary or vascular indication and intended combination duration.
06
Do not use a normal PT or APTT to conclude that clinically relevant apixaban or rivaroxaban is absent before emergency surgery or reversal.