Novel Anticoagulants
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Direct answer
Rivaroxaban, apixaban, dabigatran and edoxaban — the direct oral anticoagulants, still called novel anticoagulants or NOACs in Indian examination parlance — have displaced warfarin for most non-valvular atrial fibrillation and venous thromboembolism because they need no routine monitoring and cause roughly half the intracranial bleeding. None is decision-free: acute thrombosis has induction doses, the kidney sets cut-offs, and specific antidotes now exist — idarucizumab for dabigatran, andexanet alfa for the factor Xa inhibitors. Warfarin survives in mechanical valves, triple-positive antiphospholipid syndrome, moderate-to-severe mitral stenosis with atrial fibrillation and pregnancy, and defending that boundary is exactly what the examiner probes.
What you must remember
- Apixaban in acute venous thromboembolism: 10 mg twice daily for 7 days, then 5 mg twice daily, with no parenteral lead-in.
- Rivaroxaban: 15 mg twice daily for 21 days, then 20 mg once daily — taken with food at the 20 mg dose, which otherwise absorbs poorly.
- Dabigatran and edoxaban need 5 days of low-molecular-weight heparin first; they have no validated oral loading phase. Dabigatran is about 80% renally cleared and is avoided below a creatinine clearance of 30 mL/min.
- Apixaban falls to 2.5 mg twice daily in atrial fibrillation when two of three hold: age 80 or more, weight 60 kg or less, creatinine 1.5 mg/dL or more — the single most examined DOAC rule.
- Reversal: idarucizumab 5 g intravenously (two 2.5 g boluses) for dabigatran; andexanet alfa for apixaban and rivaroxaban; four-factor prothrombin complex concentrate 50 IU/kg is the practical fallback in most Indian centres.
- Contraindicated ground: mechanical valves (RE-ALIGN stopped early for dabigatran thrombosis), triple-positive antiphospholipid syndrome, significant mitral stenosis, pregnancy.
- Cancer-associated thrombosis: apixaban, rivaroxaban or edoxaban now sit first-line alongside low-molecular-weight heparin, with caution in luminal gastrointestinal and genitourinary malignancy that bleeds.
- INR is meaningless for DOACs. A calibrated anti-Xa assay quantifies apixaban and rivaroxaban; diluted thrombin time quantifies dabigatran.
Choosing, interrupting and reversing in one patient
A 74-year-old woman with acute pulmonary embolism, creatinine clearance 48 mL/min and weight 58 kg exercises nearly every rule. Apixaban starts at 10 mg twice daily for a week — loading doses are not trimmed for her kidneys — then settles at 5 mg twice daily. Months later she needs a cholecystectomy: for a high-bleed-risk procedure the drug is held 48 hours beforehand and resumed 24 to 48 hours after haemostasis, with neuraxial anaesthesia timed to the mandated intervals. Should she arrive with a major gastrointestinal bleed instead, the sequence is haemodynamic support, endoscopy, and andexanet alfa if it is stocked; realistically, prothrombin complex concentrate with tranexamic acid is what most Indian hospitals can deliver the same night. Haemodialysis removes only dabigatran, precisely because it is the one DOAC that barely binds plasma protein — a discriminating detail that separates the well-read candidate from the rest.
The traps examiners set
The favourite viva ploy is the mechanical mitral valve patient started on dabigatran: RE-ALIGN was stopped for increased thromboembolic events, and warfarin with an INR target near 3.0 remains correct there. The second trap is "DOACs need no monitoring" — true for anticoagulant intensity, false for renal function, which needs a creatinine every six to twelve months and sooner as clearance approaches 30 mL/min. The third is Indian-specific: rheumatic mitral stenosis with atrial fibrillation fills outpatient lists in this country, and the pivotal DOAC trials excluded it, so warfarin stays right for these patients. Claiming the drugs "cannot be measured" loses the marks that the calibrated anti-Xa answer earns.
Frequently asked questions
Which direct oral anticoagulants need a parenteral lead-in for acute venous thromboembolism?
Dabigatran and edoxaban require at least five days of unfractionated or low-molecular-weight heparin before oral monotherapy. Rivaroxaban and apixaban start at full oral loading doses from day one.
How is dabigatran specifically reversed?
Idarucizumab 5 g intravenously as two 2.5 g boluses neutralises dabigatran within minutes; haemodialysis is the alternative. The factor Xa inhibitors respond to andexanet alfa or prothrombin complex concentrate.
When is apixaban reduced to 2.5 mg twice daily in atrial fibrillation?
When at least two of three criteria are met: age 80 years or above, weight 60 kg or below, creatinine 1.5 mg/dL or above. A single criterion alone never triggers reduction.
Why does warfarin remain first-line in antiphospholipid syndrome?
Triple-positive patients — lupus anticoagulant, anticardiolipin and anti-beta-2 glycoprotein-I antibodies together — show excess thrombosis on DOACs in trial and registry data, so current guidance retains warfarin.
How is apixaban effect quantified before emergency surgery?
A calibrator-specific anti-Xa assay measures plasma apixaban; prothrombin time and INR are unreliable. Diluted thrombin time serves the same purpose for dabigatran.
Are DOACs acceptable first-line in cancer-associated thrombosis?
Current international guidance places apixaban, rivaroxaban and edoxaban alongside low-molecular-weight heparin for most cancer-associated venous thrombosis. Heparin remains preferred where bleeding risk dominates.