Anticoagulation
& thrombosis

1. Start with the indication

• Identify AF stroke prevention, acute VTE treatment, extended recurrence prevention, or prophylaxis. The same medicine can have different doses for each.
• Check bleeding, weight, renal and hepatic function, pregnancy/breastfeeding, valve disease, APS, interactions, adherence, and affordability.
• For eligible adults with AF or PE, guidelines generally favor DOACs over VKAs. Warfarin is recommended for mechanical valves and for AF with moderate-or-greater mitral stenosis. Triple-positive thrombotic APS is another important DOAC exception.
• For uncomplicated acute VTE during pregnancy, therapeutic LMWH is generally preferred. Warfarin can be used during breastfeeding, unlike its usual avoidance during pregnancy; mechanical-valve pregnancy requires specialist management.

Pause & recall
Why can a correct AF dose be an incorrect acute-DVT dose?

Sources: 2023 ACC/AHA/ACCP/HRS atrial fibrillation guideline: ACC key perspectives · 2020 ACC/AHA valve guideline: prosthetic valves · 2026 AHA/ACC multisociety acute pulmonary embolism guideline: AHA summary · XARELTO U.S. prescribing information · ASH 2018 VTE in pregnancy guideline: pocket guide

2. Keep oral-anticoagulant regimens separate

• Do not use this selected-dose table as a complete dosing monograph. Renal extremes, severe liver disease, interacting drugs, pediatric treatment, and pregnancy may change eligibility or management.
• All CrCl values in this table are in mL/min.

Pause & recall
Which two oral drugs require a parenteral lead-in for adult VTE?

Sources: ELIQUIS U.S. prescribing information, revised August 2026 · XARELTO U.S. prescribing information · PRADAXA capsules U.S. prescribing information · SAVAYSA U.S. prescribing information · Warfarin sodium U.S. prescribing information · 2020 ACC/AHA valve guideline: prosthetic valves · LOVENOX U.S. prescribing information · ASH 2020 treatment of DVT and PE guideline

3. Heparins, dosing, and HIT

• UFH infusions: verify units/kg/hour, actual bag concentration, pump rate, and protocol-specific coagulation monitoring. Never confuse units/hour with mL/hour.
• Selected enoxaparin acute-DVT regimen: 1 mg/kg subcutaneously every 12 hours. For CrCl <30 mL/min, the labeled DVT treatment regimen with warfarin is 1 mg/kg subcutaneously every 24 hours. Acutely ill medical prophylaxis uses 40 mg subcutaneously daily, reduced to 30 mg subcutaneously daily at CrCl <30 mL/min.
• Fondaparinux adult DVT/PE treatment, all subcutaneously: <50 kg → 5 mg daily; 50–100 kg → 7.5 mg daily; >100 kg → 10 mg daily. It is contraindicated at CrCl <30 mL/min; the 2.5-mg prophylaxis regimen is separate.
• Use the 4Ts to assess suspected HIT. A reliable low-probability score generally avoids routine testing and empiric HIT treatment. High probability requires stopping all heparin exposure and starting appropriate non-heparin anticoagulation while testing proceeds.
• Do not replace UFH with LMWH in acute HIT. Delay warfarin until platelet recovery, usually ≥150 × 10^9/L. Agent selection and intensity depend on the clinical situation; argatroban needs particular attention to hepatic function.

Pause & recall
Why is switching from UFH to enoxaparin unsafe in acute HIT?

Sources: LOVENOX U.S. prescribing information · ARIXTRA U.S. prescribing information, revised December 2024 · ASH diagnosis and management of HIT pocket guide · Argatroban U.S. prescribing information · Heparin sodium and dextrose U.S. prescribing information

4. Monitor and counsel

• Warfarin: INR-guided dosing, consistent dietary vitamin K, and earlier INR reassessment when interacting drugs or major dietary/health changes occur. Do not automatically use a fixed dose reduction for every interaction.
• DOACs: no routine INR titration. Reassess bleeding, blood count, renal function, clinically relevant hepatic changes, interactions, adherence, and ongoing indication. Monitoring frequency depends on clinical risk and changes.
• Apixaban plus strong combined CYP3A4/P-gp inducers such as carbamazepine: avoid. With strong combined inhibitors, check the exact dose and label; already taking 2.5 mg twice daily is an important avoid-combination situation.
• Ask before adding NSAIDs, aspirin, or supplements. Multiple antithrombotics need a documented indication and planned duration.
• Missed doses differ: apixaban → take as soon as possible the same day without doubling; dabigatran → skip if fewer than 6 hours remain before the next dose; rivaroxaban 15 mg twice daily has its own same-day 30-mg recovery instruction.
• Urgent symptoms include severe headache with neurologic change, vomiting blood, black tarry stool, or new neurologic symptoms after a spinal procedure.

Pause & recall
What still needs monitoring when a medicine does not require INR checks?

Sources: Warfarin sodium U.S. prescribing information · ELIQUIS U.S. prescribing information, revised August 2026 · PRADAXA capsules U.S. prescribing information · XARELTO U.S. prescribing information · ASH optimal management of anticoagulation pocket guide · ASH 2018 optimal management of anticoagulation guideline · NHS Specialist Pharmacy Service DOAC monitoring, updated August 6, 2026

5. Bleeding and reversal

Pause & recall
Why does PCC treatment of warfarin bleeding also need vitamin K?

Sources: ASH optimal management of anticoagulation pocket guide · KCENTRA U.S. prescribing information · LOVENOX U.S. prescribing information · FDA update on Andexxa safety, December 18, 2025 · CHEST evidence-based management of anticoagulant therapy, 2012 · PRAXBIND U.S. prescribing information

6. Transitions, procedures, and duration

• Write the last dose, first dose, and monitoring plan when changing anticoagulants. For warfarin → apixaban, begin apixaban when INR is <2.0. Do not generalize this threshold to every DOAC.
• Acute-VTE warfarin initiation: overlap therapeutic UFH/LMWH for at least 5 days and until INR has been therapeutic for at least 24 hours, with patient-specific protocol verification.
• For an elective procedure, consider drug, renal function, bleeding risk, thrombotic risk, and neuraxial plans. Routine therapeutic heparin bridging is unnecessary for a short DOAC interruption. Restart requires an explicit plan and adequate hemostasis.
• A first VTE associated with a resolved major transient risk factor may finish after the primary course, with reassessment. For a first PE without a major reversible risk factor, the 2026 guideline recommends extended anticoagulation beyond the initial 3–6 months.
• Active cancer may favor ongoing treatment; reassess bleeding, interactions, tumor site, and preferences. In AF with stable coronary disease >1 year after revascularization and no stent-thrombosis history, guideline-directed OAC monotherapy can avoid unnecessary aspirin exposure.

Pause & recall
How does bridging during acute-VTE warfarin initiation differ from an elective DOAC interruption?

Sources: ELIQUIS U.S. prescribing information, revised August 2026 · LOVENOX U.S. prescribing information · ACC perioperative DOAC management, August 2024; interruption and bridging sections only · 2026 AHA/ACC multisociety acute pulmonary embolism guideline: AHA summary · ASH treatment of VTE in patients with cancer pocket guide · 2023 ACC/AHA/ACCP/HRS atrial fibrillation guideline: ACC key perspectives · ASH treatment of DVT and PE guideline · ASH 2020 treatment of DVT and PE guideline

7. A quick calculation check

• Infusion: ordered units/hour ÷ bag units/mL = mL/hour. Example: 1,500 units/hour ÷ 100 units/mL = 15 mL/hour.
• Weight-based injection: kg × mg/kg = mg per dose; then divide by mg/mL. Example: 86 kg × 1 mg/kg ÷ 100 mg/mL = 0.86 mL.
• Changing oral regimens: calculate each phase separately. Use the actual tablet strength and the exact requested number of days.
• Round only at the final step using the requested precision; reverse-check the answer against the original prescribed dose.

Pause & recall
Does your final unit answer the question that was asked?

Sources: LOVENOX U.S. prescribing information · Heparin sodium and dextrose U.S. prescribing information

Abbreviations

AF

atrial fibrillation

VTE

venous thromboembolism

DVT

deep vein thrombosis

PE

pulmonary embolism

DOAC

direct oral anticoagulant

VKA

vitamin K antagonist

CrCl

creatinine clearance

INR

international normalized ratio

UFH

unfractionated heparin

LMWH

low-molecular-weight heparin

HIT

heparin-induced thrombocytopenia

PCC

prothrombin complex concentrate

APS

antiphospholipid syndrome

OAC

oral anticoagulant

NSAIDs

nonsteroidal anti-inflammatory drugs

IV

intravenous

aPTT

activated partial thromboplastin time

P-gp

P-glycoprotein

CYP3A4

cytochrome P450 3A4

4Ts

HIT probability assessment: thrombocytopenia, timing, thrombosis, and other causes