Anticoagulation Therapy

Meet the patient

A 78-year-old woman on apixaban for atrial fibrillation is brought in confused after a fall, with a large left temporal haematoma. Her CT shows an intracerebral haemorrhage. The registrar asks the right question first: which anticoagulant, when was the last dose, and what is her renal function?^[6]

The answer — apixaban, taken 4 hours ago, eGFR 45 — decides the next minute. You do not wait for an anti-Xa level; you reach for andexanet alfa while the neurosurgeons are called, because the haematoma will keep expanding for as long as the drug is active. Had she been on warfarin the answer would have been vitamin K plus PCC; on dabigatran, idarucizumab. The agent names the antidote.^[6][7]

What anticoagulants do — and the four questions before you prescribe

Anticoagulants prevent and treat thromboembolic disease by interfering with the coagulation cascade at specific points. Four questions must be answered before any prescription: (1) what is the thrombotic risk without anticoagulation (the indication)? (2) what is the bleeding risk? (3) what renal and hepatic function does the patient have (it dictates dose and drug)? (4) what else are they on (interactions)? Skipping any one of these is how patients come to harm.^[1]

The four classes are the parenteral heparins (unfractionated heparin and low-molecular-weight heparin, which potentiate antithrombin), the vitamin K antagonist warfarin (which impairs gamma-carboxylation of factors II, VII, IX, X and protein C and S), and the direct oral anticoagulants (DOACs) — dabigatran (a direct thrombin or IIa inhibitor) and rivaroxaban, apixaban, edoxaban (direct factor Xa inhibitors).^[1]

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The drug classes — mechanisms, monitoring, and the doses you must own

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Warfarin — the vitamin K antagonist

Warfarin inhibits VKORC1, so factors II, VII, IX, X and protein C and S are not gamma-carboxylated and remain inactive. Its onset is slow (3 to 5 days) because factor II (prothrombin) has a half-life of 60 to 72 hours — which is why you bridge with LMWH for any major indication until the INR is in range for two consecutive days. It is monitored by INR and reversed by vitamin K plus PCC.^[1]

INR targets (reproduce verbatim):^[1]

• 2.0 to 3.0 — AF, VTE (treatment), antiphospholipid syndrome, cardiomyopathy with thrombus, mural thrombus, mechanical aortic bileaflet valve without risk factors.
• 2.5 to 3.5 — mechanical mitral or tricuspid valve, recurrent VTE despite INR 2 to 3, mechanical aortic valve with risk factors.^[1]

Warfarin initiation: randomised comparison of 10-mg versus 5-mg initiation nomograms in outpatient VTE (both with LMWH cover) found the 10-mg nomogram reached a therapeutic INR 1.4 days faster — 83 percent therapeutic by day 5 versus 46 percent — with no excess of INR values over 5, bleeding, or recurrent events. LMWH is continued for at least 5 days and until the INR is therapeutic.^[8]

INR monitoring schedule: check INR on day 3, then every 2 to 3 days for the first week, weekly for the second, then every 2 weeks, stretching to every 4 to 12 weeks once stable. Time in Therapeutic Range (TTR) — the proportion of INR readings in range; TTR under 65 percent indicates poor control, prompting a DOAC switch or attention to adherence and interactions.^[1]

Heparins — UFH and LMWH

Unfractionated heparin (UFH) potentiates antithrombin and is monitored by aPTT. The weight-based nomogram — 80 units per kg IV bolus, then 18 units per kg per hour infusion — reaches therapeutic anticoagulation faster than standard-care dosing; aPTT is checked every 6 hours and the dose adjusted to a therapeutic aPTT of 1.5 to 2.3 times control.^[10]

Low-molecular-weight heparin (enoxaparin) — for acute DVT the trial-tested regimen is 1 mg per kg subcutaneously twice daily, continued for at least 5 days and until the vitamin K antagonist raises the INR above 2.0.^[11] LMWH is given once or twice daily by subcutaneous injection without routine coagulation monitoring, with more predictable pharmacokinetics than UFH and a lower risk of heparin-induced thrombocytopenia and osteoporosis.^[30] For prophylaxis after hip arthroplasty, the trial-tested dose is 40 mg subcutaneously once daily (comparator arm of the rivaroxaban prophylaxis trials).^[15]

Direct oral anticoagulants (DOACs) — no routine monitoring, rapid onset, missed doses matter

DOACs need no routine monitoring, have rapid onset (1 to 3 hours) and a short half-life (so missed doses matter). Renal function is checked at least annually, more often in CKD.^[1]

Dabigatran (Pradaxa) — direct IIa inhibitor, dosed as fixed 110 mg or 150 mg twice daily in atrial fibrillation. In RE-LY, 150 mg twice daily reduced stroke or systemic embolism versus warfarin (1.11 vs 1.69 percent per year) with similar major bleeding, while 110 mg twice daily was non-inferior with less major bleeding (2.71 vs 3.36 percent per year); both doses cut haemorrhagic stroke. Reversed by idarucizumab.^[3]

Rivaroxaban (Xarelto) — direct Xa inhibitor. AF: 20 mg oral once daily (non-inferior to warfarin for stroke prevention, with fewer intracranial and fatal haemorrhages); 15 mg once daily if creatinine clearance 30 to 49 mL per min.^[12][13] VTE treatment: 15 mg twice daily for 3 weeks, then 20 mg once daily — as effective as enoxaparin plus vitamin K antagonist, without laboratory monitoring.^[14] Thromboprophylaxis after hip arthroplasty: 10 mg once daily, superior to enoxaparin 40 mg daily.^[15]

Apixaban (Eliquis) — direct Xa inhibitor. AF: 5 mg twice daily — superior to warfarin for stroke prevention with less major bleeding (2.13 vs 3.09 percent per year) and lower mortality; reduce to 2.5 mg twice daily if at least 2 of: age 80 or over, weight 60 kg or less, creatinine 1.5 mg per dL or more.^[4][29] VTE treatment: 10 mg twice daily for 7 days, then 5 mg twice daily (AMPLIFY); for extended treatment after 6 to 12 months, 2.5 mg twice daily reduced recurrent VTE without increasing major bleeding (AMPLIFY-EXT).^[16][17]

Edoxaban (Lixiana or Savaysa) — direct Xa inhibitor. VTE treatment after initial heparin: 60 mg oral once daily, reduced to 30 mg once daily if creatinine clearance 30 to 50 mL per min or weight under 60 kg — non-inferior to warfarin with less clinically relevant bleeding (Hokusai-VTE).^[18] In AF (ENGAGE AF-TIMI 48) both once-daily edoxaban regimens were non-inferior to warfarin for stroke prevention with significantly lower rates of bleeding and cardiovascular death.^[19]

Fondaparinux (Arixtra) — synthetic pentasaccharide, indirect (antithrombin-mediated) Xa inhibitor. Initial DVT treatment: 7.5 mg subcutaneously once daily — 5 mg if body weight under 50 kg, 10 mg if over 100 kg — as effective as enoxaparin 1 mg per kg twice daily.^[11] Predictable effect, no routine monitoring, few drug interactions; heparin-induced thrombocytopenia appears rare with pentasaccharides.^[31]

^{[4] [29] [22] [7]}

Indications and the agent that fits each

The agent choice is dictated by the indication and by patient factors (renal function, valves, pregnancy, cancer). Reproduce this table for the exam:^[1]

^{[2] [21] [5]}

Risk scores — CHA2DS2-VASc and HAS-BLED (reproduce the components)

Thrombotic risk in AF — CHA2DS2-VASc: Congestive heart failure (1), Hypertension (1), Age 75 or over (2), Diabetes (1), Stroke or TIA or thromboembolism (2), Vascular disease (prior MI, PAD, aortic plaque — 1), Age 65 to 74 (1), Sex category female (1). Anticoagulate at score 2 or more in men, 3 or more in women (NICE NG196). The annual stroke risk in untreated AF rises from about 1 percent (score 0) to about 12 percent (score 8); anticoagulation reduces stroke by about 64 percent.^[1]

Bleeding risk — HAS-BLED: Hypertension uncontrolled (SBP over 160, 1), Abnormal renal or liver function (1 each, max 2), Stroke history (1), Bleeding history or predisposition (1), Labile INR — TTR under 60 percent (1), Elderly age over 65 (1), Drugs or alcohol concomitantly — antiplatelets, NSAIDs, excess alcohol (1). Score 3 or more = high bleeding risk — this does NOT contraindicate anticoagulation; it prompts correction of modifiable factors (BP, NSAIDs, alcohol) and DOAC preference over warfarin (lower intracranial haemorrhage).^[1]

Clinical and bedside assessment

Assessment of a patient on (or about to start) anticoagulation covers four domains. (1) Thrombotic risk — the indication and the risk without anticoagulation (CHA2DS2-VASc for AF; Caprini for surgical VTE risk; Padua for medical inpatients; mechanical valve position). (2) Bleeding risk — HAS-BLED, concurrent antiplatelets, recent surgery, active ulcer, recent intracranial haemorrhage. (3) Renal and hepatic function — eGFR dictates DOAC dose and LMWH safety; cirrhosis with synthetic failure makes warfarin hazardous. (4) Drug history and interactions — warfarin interacts with hundreds via CYP2C9 (macrolides, metronidazole, fluconazole, amiodarone, statins, NSAIDs, SSRIs); DOACs interact via P-glycoprotein (verapamil, dronedarone, clarithromycin, rifampicin, St John's wort, ketoconazole, antiepileptics); antiplatelets and NSAIDs add bleeding risk.^[1]

Investigations

Baseline investigations before starting any anticoagulant: full blood count (platelets for HIT detection; haemoglobin for bleeding surveillance), coagulation screen (PT or INR, aPTT, fibrinogen, thrombin time — markedly prolonged by dabigatran), U&E and creatinine or eGFR (DOAC dosing and LMWH clearance; recheck at least annually, every 3 to 6 months in CKD, after acute illness, or when changing interacting drugs), LFTs, group and save (for high-risk initiation), urinalysis (baseline haematuria — occult malignancy is not uncommonly detected), and a pregnancy test in any woman of childbearing potential before warfarin or a DOAC.^[1]

Drug-specific monitoring: for warfarin, INR per the schedule above; for UFH, aPTT (or anti-Xa) 6 hours after each dose change, target 1.5 to 2.5 times control; for LMWH, no routine monitoring (anti-Xa only in pregnancy, extremes of weight, severe renal impairment, or children); for DOACs, no routine monitoring — but a normal thrombin time excludes clinically relevant dabigatran and a normal anti-Xa excludes clinically relevant rivaroxaban or apixaban, useful before emergent surgery. Do NOT use INR or aPTT to monitor DOACs — they may be minimally affected and are misleading.^[1]

Investigating a bleeding patient on anticoagulant: INR (warfarin), renal function (DOAC clearance), FBC, group and crossmatch, coagulation screen, fibrinogen. Imaging at the bleeding source — CT head for any suspected intracranial haemorrhage (do NOT delay reversal for imaging — clinical suspicion of intracranial bleed alone justifies empirical reversal). Send for occult malignancy workup if unprovoked bleeding at a site (colonoscopy for lower GI bleed, cystoscopy for frank haematuria).^[1]

Management — resuscitation of the major anticoagulant bleed

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Major bleeding on anticoagulation is a medical emergency. The bundle: stop the drug, local control, reversal, resuscitation, find the source.^[1][6][7]

^{[20] [7] [6] [9] [20] [7] [6] [28]}

Warfarin reversal by scenario (trial-tested):^[9][20]

• INR 4.5 to 10, no bleeding — withhold warfarin and give low-dose ORAL vitamin K (1 mg in the randomised trial): oral vitamin K restored a therapeutic INR on the next day far more often than subcutaneous vitamin K (15 of 26 vs 6 of 25 patients).^[9]
• Major bleeding on a vitamin K antagonist — four-factor PCC (contains factors II, VII, IX, X and proteins C and S): in a randomised trial versus plasma it achieved effective 24-hour haemostasis in 72.4 percent and corrected INR to 1.3 or less within 30 minutes of the infusion far more often than plasma.^[20]

Management — definitive and stepwise: peri-operative and counselling

Peri-operative management: for warfarin, stop 5 days pre-op, check INR under 1.5 on the day of surgery; bridge with LMWH if high thrombotic risk (mechanical mitral valve, recent VTE under 3 months, stroke under 3 months, AF with CHA2DS2-VASc over 6); restart warfarin on day 1 to 2 post-op when haemostasis secure. For DOACs, stop 24 to 48 hours pre-op (48 hours if high bleed risk or eGFR under 50); restart 24 hours after low-bleed-risk surgery, 48 to 72 hours after high-bleed-risk surgery. No bridging — DOACs have rapid onset.^[1]

Counselling (every patient on an anticoagulant must know): bleeding signs to report (unexplained bruising, prolonged bleeding from cuts, blood in urine or stool or vomit, severe headache, joint pain or swelling); drug interactions (warfarin — inform every prescriber, carry an anticoagulant card); missed dose (warfarin — take if remembered the same day, skip if next day; DOAC — take if remembered within half the dosing interval, skip if closer to next dose; never double up); diet (warfarin — consistent vitamin K intake, do not start or stop broccoli, spinach, Brussels sprouts; cranberry juice can increase INR); alcohol (avoid binge — acutely raises INR); surgery or dental (most dental work does not require stopping — use local measures); pregnancy (warfarin switched before 6 weeks gestation to LMWH; contraception counselling).^[1]

The three classic complications — HIT, warfarin necrosis, and DOAC bleeds

Heparin-induced thrombocytopenia (HIT) — the exam classic

Type I (non-immune) — mild platelet drop in first 4 days, benign, no action. Type II (immune) — IgG antibody against the heparin-PF4 complex activates platelets to both thrombosis and thrombocytopenia. Onset 5 to 14 days after starting heparin (or sooner if prior heparin in 30 days — "rapid onset HIT"); platelets fall 50 percent or to below 150, nadir usually above 10 (distinguishes from DIC, TTP). Paradoxical thrombosis is the danger — venous (DVT, PE, limb gangrene, adrenal haemorrhage) and arterial (limb ischaemia, stroke, MI). Mortality 20 to 30 percent if untreated.^[1]

Diagnosis — the 4Ts score: Thrombocytopenia (0 to 2), Timing of platelet fall (0 to 2), Thrombosis or other sequelae (0 to 2), Therapeutic alternatives (oTher cause, 0 to 2). Score 0 to 3 = unlikely (do not treat); 4 to 8 = possible HIT — send anti-PF4 ELISA or serotonin release assay, and START treatment.^[1]

Management: STOP ALL HEPARIN (UFH, LMWH, heparin flushes, heparin-coated lines). Start a non-heparin anticoagulant — argatroban (hepatic clearance — preferred in renal failure; aPTT monitored) or danaparoid or bivalirudin (renal). Do NOT give platelet transfusion (fuels thrombosis). Do NOT give warfarin alone initially — can cause venous limb gangrene (skin-necrosis-like); only start warfarin once platelets are recovering AND continue the non-heparin agent for overlap until platelets normal AND INR in range for 2 days. Re-exposure to heparin: only if life-saving and previous HIT over 100 days ago (antibodies usually fade).^[1]

Warfarin-induced skin necrosis

Warfarin-induced skin necrosis is a rare complication of anticoagulant therapy with high morbidity and mortality, requiring immediate drug cessation. Cutaneous findings are petechiae progressing to ecchymoses and haemorrhagic bullae; dermatopathology shows diffuse dermal microthrombi with endothelial cell damage and red-cell extravasation, progressing to full-thickness coagulative necrosis. Diagnosis is clinical plus biopsy.^[24] The syndrome typically occurs during the first few days of warfarin therapy, often in association with a large initial loading dose, and better understanding of the protein C, protein S and antithrombin III pathways explains the transient prothrombotic mechanism.^[25]

Bleeding on DOACs and other complications

Bleeding is the dominant complication. In an individual patient-data meta-analysis of the four pivotal DOAC-versus-warfarin AF trials (71,683 patients), standard-dose DOACs versus warfarin reduced intracranial bleeding from 1.40 to 0.63 percent (hazard ratio 0.45), stroke or systemic embolism from 3.69 to 3.01 percent, and showed less major bleeding (5.05 vs 5.94 percent) — the intracranial-haemorrhage reduction is a major reason DOACs are first-line in AF.^[26]

The classic pitfalls: treating INR with vitamin K too aggressively when minimally elevated (5 to 8, no bleed) — causes prolonged warfarin resistance then rebound thrombosis; not bridging warfarin for high-thrombotic-risk indications when interrupting for surgery; bridging DOACs (unnecessary — rapid onset — increases bleeding); forgetting that DOACs need renal dose adjustment with acute illness; continuing DOACs peri-operatively at full dose in renal impairment; misreading a normal PT or INR as "DOAC safe" for surgery (insensitive — use anti-Xa or wait longer); not investigating the source of bleed (occult colorectal cancer in up to 5 to 10 percent presenting with lower GI bleed on anticoagulation).^[1]

Special populations

Pregnancy — the highest-yield special population

Anticoagulation in pregnancy (ACCP guidelines): for pregnant women in general, vitamin K antagonists should be substituted with unfractionated heparin (UFH) or low-molecular-weight heparin (LMWH) (Grade 1A), except perhaps in women with mechanical heart valves.^[21] For pregnant patients, LMWH is suggested over UFH for the prevention and treatment of VTE (Grade 2C); for acute VTE in pregnancy, subcutaneous LMWH or UFH should be continued throughout pregnancy, with anticoagulation continued for at least 6 weeks postpartum (minimum total duration 6 months).^[21]

Renal impairment

Kidney function drives both safety and dose. In an individual patient-data analysis of the four pivotal DOAC-versus-warfarin AF trials, rates of stroke, major bleeding, intracranial haemorrhage and death all rose with worsening kidney function, yet standard-dose DOACs remained safer and more effective than warfarin down to a creatinine clearance of at least 25 mL per min — lower-dose DOACs did not reduce bleeding or intracranial haemorrhage versus standard-dose but had more stroke/systemic embolism and death.^[27] Agent-specific renal dose reductions remain agent- and label-specific — e.g. rivaroxaban 15 mg once daily at creatinine clearance 30 to 49 mL per min.^[13]

Hepatic impairment

Warfarin problematic — already elevated INR from synthetic failure; a small additional dose may overshoot. DOACs — contraindicated in Child-Pugh C cirrhosis (apixaban, rivaroxaban); caution in Child-Pugh B; LMWH preferred. Portal vein thrombosis in cirrhosis — DOACs increasingly used if low bleed risk; consider warfarin or LMWH.^[1]

Elderly (over 75)

Apixaban (5 mg twice daily) has the strongest trial evidence in this group — ARISTOTLE showed superiority to warfarin for stroke prevention with less major bleeding (2.13 vs 3.09 percent per year) and lower all-cause mortality, and it is given twice daily.^[4]

Mechanical heart valve (the absolute warfarin-only scenario)

Warfarin INR 2.5 to 3.5 for mitral (caged-ball, tilting disc, or bileaflet with risk factors) and tricuspid; 2.0 to 3.0 for aortic bileaflet without risk factors. The RE-ALIGN trial (2013) randomised mechanical valve patients to dabigatran versus warfarin — stopped early because dabigatran had more thromboembolic events (valve thrombosis, stroke) AND more bleeding. ALL DOACs are contraindicated in mechanical valves.^[5]

Paediatric anticoagulation

Anticoagulation in neonates and children differs from adults: manage with, or in consultation with, a paediatric haematologist experienced in thromboembolism. Therapeutic UFH is titrated to a target anti-Xa of 0.35 to 0.7 units per mL (or an aPTT range correlating with it); therapeutic LMWH — daily or twice daily — is monitored with an anti-Xa sample taken 2 to 6 hours after subcutaneous injection.^[23] Most paediatric recommendations extrapolate adult data, and the underlying evidence remains weak.^[23]

Prognosis and disposition

Anticoagulation reduces AF-related stroke by about 64 percent and all-cause mortality by about 26 percent. In VTE, it reduces recurrence from about 50 percent per year (untreated) to under 5 percent per year. The net clinical benefit (stroke prevented minus major bleeding) is positive for most patients with AF and CHA2DS2-VASc of 2 or more, even in the elderly and at higher bleeding risk. Major bleed prognosis — 30-day mortality of warfarin-related intracranial haemorrhage is about 50 percent; rapid reversal (within 1 to 2 hours) with PCC improves outcomes (FFP is too slow). DOAC-related intracranial haemorrhage has slightly better prognosis (smaller haematoma expansion).^[1]

Duration of anticoagulation: provoked VTE (surgery, fracture, immobility, oestrogen) — 3 months, then stop. Unprovoked VTE — at least 3 months; consider indefinite. Cancer-associated VTE — lifelong while cancer active. AF — lifelong. Mechanical valve — lifelong. APS first VTE — lifelong. Disposition: DOAC initiation can be outpatient for stable AF or low-risk DVT (rivaroxaban, apixaban — no parenteral lead-in). Warfarin initiation in VTE requires bridge with LMWH (5 days) — often outpatient via LMWH. Hospital admission for massive PE, intracranial haemorrhage or major bleed, HIT, or first presentation requiring aggressive workup. ICU for haemodynamic instability, intracranial bleed, or HIT with thrombosis.^[1]

Evidence — the landmark trials you must name

^{[3] [4] [5] [6] [7] [2]}

The mantra

Mechanical valve means warfarin; pregnancy means LMWH; HIT means argatroban; and the agent names the antidote — idarucizumab for dabigatran, andexanet for the Xa inhibitors, vitamin K plus PCC for warfarin.^[1][5]

Ward-round test

Stem 1 — the intracranial bleed on warfarinShowHide

A 72-year-old on warfarin for a mechanical mitral valve (INR 7.2) has an intracerebral haemorrhage. What is the reversal bundle, and what must you NOT do?^[1]

AnswerShowHide

STOP warfarin and give four-factor PCC immediately — in the randomised trial versus plasma, 4F-PCC (factors II, VII, IX, X plus proteins C and S) achieved effective 24-hour haemostasis in 72.4 percent and corrected the INR to 1.3 or less within 30 minutes of the end of infusion — with resuscitation, CT, and neurosurgery. Do NOT delay reversal for imaging if intracranial bleed is suspected. Because this is a mechanical mitral valve, restarting anticoagulation once stable is essential, and it means warfarin — no DOAC (RE-ALIGN showed excess thromboembolic and bleeding events with dabigatran in mechanical valves).^[20][5]

Stem 2 — the falling platelets after heparinShowHide

A postoperative patient on LMWH for DVT prophylaxis has platelets falling from 280 to 90 on day 8, and develops a new swollen leg. What is the diagnosis and the first three actions?^[1]

AnswerShowHide

Heparin-induced thrombocytopenia (HIT) — platelet fall over 50 percent, 5 to 14 days after heparin, with thrombosis not bleeding. (1) STOP ALL heparin (including flushes and heparin-coated lines). (2) Start a non-heparin anticoagulant — the ACCP suggests argatroban, lepirudin or danaparoid for HIT with normal renal function, and argatroban in renal insufficiency. (3) Send anti-PF4 ELISA and a functional serotonin-release assay, and calculate the 4Ts score. Do NOT transfuse platelets; do NOT start warfarin alone until platelets recover.^[22]

Stem 3 — the apixaban bleedShowHide

A 78-year-old on apixaban 5 mg BD (eGFR 45) has a major GI bleed. What is the specific antidote?^[6]

AnswerShowHide

Andexanet alfa — a recombinant modified human factor Xa decoy protein that binds and sequesters the Xa inhibitor — given as an initial bolus followed by a 2-hour infusion. In ANNEXA-4 (mean age 77; bleeding predominantly gastrointestinal or intracranial) the median anti-Xa activity fell by 93 percent in apixaban-treated patients and effective hemostasis occurred in 79 percent. Stop the apixaban, resuscitate, and find the bleeding source.^[6][28]

Stem 4 — the pregnant patient with a mechanical valveShowHide

A 30-year-old with a mechanical mitral valve is 5 weeks pregnant and on warfarin. What must change, and why?^[21]

AnswerShowHide

Substitute the vitamin K antagonist with LMWH (or UFH) in pregnancy — the ACCP recommends this substitution for pregnant women in general (Grade 1A), with LMWH preferred over UFH and treatment continued throughout pregnancy and for at least 6 weeks postpartum; women with mechanical heart valves are the acknowledged exception in whom management must be individualised, because RE-ALIGN showed dabigatran (and by extension DOACs) carry excess thromboembolic and bleeding risk in mechanical valves.^[21][5]

References32ShowHide

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