New Oral Anticoagulants

1. NOACs
Dr Carolyn Grove
Clinical and Laboratory Haematologist
Sir Charles Gairdner Hospital and
PathWest Laboratory Medicine

2. Overview
• Expected coagulation parameters in the setting of
DOACs
– Do these correlate with bleeding risk?
• Treatment of bleeding
Although NOACs are no longer novel, there is still surprisingly
limited evidence on which to base Rx decisions

3. Coagulation Cascade
PL – Platelet Membrane Phospholipid
TF - Tissue Factor
‘a’ – active enzyme
Rivaroxaban/Apixaban
Dabigatran
Mechanistically different
from warfarin
•Warfarin indirect
effect by interfering
with Vit K metabolism
•Act at catalytic
pocket of coagulation
factors and inhibit
their function

4. Tran et al, New Oral Anticoagulants: a practical guide IMJ 44 (2014)

5. Case 1
• Pre-op assessment
• No other history
Test Result Reference Range
APTT 49.7s 29.5-40.5s
INR 2.29 0.9-1.3
TCT 18.3s 15-23s
Fibrinogen 4.35g/L 2-4.1g/L
APTT 50:50 36.2s 29.5 - 40.5s
INR 50:50 1.35 0.9-1.3

6. Case 1
Test Result Reference Range
FX 69% 70-140%
FII 71% 65-130%
FV 32% 65-140%
FVII 62% 65-135%
FVIII 76% 50-200%
FIX 58% 50-200%
FXI 52% 65-140%
Rivaroxaban 348ng/mL

7. Case 1: Discussion Points
• What does the rivaroxaban level mean?
• Is this a typical picture for coagulation parameters on
therapeutic rivaroxaban?

8. Rivaroxaban
• Peak levels within 3h of ingestion
• Quantified by calibrated anti-Xa assays using
rivaroxaban standards
– 20mg OD dose:
• Peak 290ng/mL (range 177-409 5-95th
centile)
• Trough 32ng/mL (range 5-155ng/mL)
– 10mg OD dose:
• Peak 125ng/mL (range 91-196)
• Trough 9ng/mL (1-38)

9. PT
APTT
Tests: PT and APTT
Principles….
Citrated blood
Centrifuged -> Platelet poor plasma
+ Activator
+ Platelet substitute
+ Calcium
->Measure time to clot formation

10. Rivaroxaban and Coags
Hillarp et al. Journal of Thrombosis and Haemostasis, 9: 133-139

11. Rivaroxaban and routine
coagulation assays
• PT more suitable than APTT for assessing
anticoagulation intensity
– Linear over broad range and high sensitivity
– Marked variability between reagents (3x)
– Can be used to determine relative degree of anticoagulation if
sensitivity of PT known
• Normal PT ratio with most reagents excludes a
therapeutic intensity of anticoagulation due to
rivaroxaban
– Some degree of anticoagulation not excluded
– Intensity ≤ prophylactic dose of LMWH

12. Ex vivo experiment with
rivaroxaban (10 mg)
Asmis, L.M. et al Thrombosis Research 129 (2012) 492-498

13. Rivaroxaban
• TT, fibrinogen not affected
• No effect on D-dimer assay
– Suppression of D-dimer levels due to inhibition of thrombin
generation
• LAC assay is sensitive to low levels of rivaroxaban

14. Case 2
78 y.o. man
A&E
0-1
D/C
Coronary
angiography
and drug
eluting stent
Ticagrelor +
aspirin
-40 -8
Right upper
lobectomy
and wedge
lower lobe
resection
-7
AF+ HD
instability
-5
Chest pain
No new
changes on
angiogram
-4
Start
apixaban
5mg bd

15. A&E
• Dyspnoea and collapse
• New right pleural effusion and right anterior chest wall
haematoma
• Apixaban last dose 17hours ago
• Hb 123, plt 579, INR 2.7, APTT 41.7s
• Apixaban 139.7ng/mL

16. Management Case 2
• Stop antiplatelet and apixaban Rx
• 25IU/kg prothrombinex
• 1U platelets
• Apixaban 36 hours post dose 55.9ng/mL
• INR 2.8, APTT 52.9, normal liver and renal function
• Factors
– VII = 25%
– X = 54%
– XI = 38%
• Vitamin K 10mg IV with normalisation of coag profile and
factors

17. Case 2 Discussion Points
• Were the apixaban levels and time course for drug
clearance typical?
• Were the abnormalities in coagulation profiles consistent
with apixaban therapy?

18. Apixaban Levels
10mg single dose fasted v fed
Frost C et al. Br J Clin Pharmacol. 2013 Feb;75(2):476-87

19. Apixaban levels
• APPRAISE-1 study ACS 10mg bd doses
– 2.5mg bd dose
• Peak 68ng/mL (38 / 98 5th
/95th
percentile)
• Trough 57ng/mL (18 / 97 5th
/95th
percentile)
– 5mg bd dose
• Trough 107ng/mL (56 / 203 10th
/90th
percentile)
– 10mg bd dose
• Peak 267ng/mL (122 / 412 5th
/95th
percentile)
• Trough 221ng/mL (30 / 412 5th
/95th
percentile)
• Our lab limits of detection 20-999 ng/mL

20. Apixaban
Hillarp, A et al. Journal of Thrombosis and Haemostasis (2014), 12: 1-9
At peak of
200ng/mL most
responses were
within the
reference interval
for APTT for that
reagent.
Even at peak
1000ng/mL APTT
still within
reference limit for
several samples.

21. Apixaban concentration to
double APTT
Hillarp, A et al. Journal of Thrombosis and haemostasis, 12: 1-9

22. Apixaban and INR
Hillarp, A et al. Journal of Thrombosis and haemostasis, 12: 1-9

23. Hillarp, A et al. Journal of Thrombosis and Haemostasis, 12: 1-9

24. Apixaban
• Cannot use APTT or PT to screen for apixaban activity
– They may be normal even with peak apixaban levels
• Concentration needed to double
– APTT = 2200 - 4700ng/mL (5-6x rivaroxaban)
– PT = 700 - 3900ng/mL (2-7x rivaroxaban)
• Linear dose response curves for chromogenic anti-FXa
assays
– this is the way to check if drug on board
• If markedly deranged PT/APTT consider other causes
Hillarp, A et al. Journal of Thrombosis and Haemostasis, 12: 1-9

25. • No obvious explanation for differences between
rivaroxaban and apixaban in vitro.

26. Case 2 Discussion Points
• Were the apixaban levels and time course for drug
clearance typical?
• Were the abnormalities in coagulation profiles consistent
with apixaban therapy?

27. Case 3
• CHADS score 4
• Previous bleeding on warfarin
• Changed to dabigatran
• Presented by ambulance after first dose rivaroxaban
(reason for change unclear)
• Felt tongue swelling and tightness in throat immediately
after first dose

28. Case 3
Test Result +4hrs Result + 14 Reference
Range
APTT 73.1 32.2 29.5-40.5s
INR 4.3 1.7 0.9-1.3
TCT >120 15-23s
Fibrinogen 3.4 3.38 2-4.1g/L
Rivaroxaban 490 102.3
Dabigatran 226 64

29. Dabigatran
• Peak 2h post ingestion
• 150mg bd dose
– mean peak plasma concentration 175ng/mL with range 117-
275ng/mL (25th
-75th
percentile range)
• Our lab 50-500ng/mL

30. Dabigatran
• APTT curvilinear dose-response with dabigatran
– Steep increase at low concentrations
– linearity above dabigatran of 200ng/mL
• Above 100ng/mL the APTT is invariably prolonged
• A normal APTT ratio likely excludes a therapeutic
intensity of anticoagulation
– Can’t exclude some effect
– Intensity no more than with prophylactic LMWH
• Even at 200ng/mL the PT is not prolonged or prolonged
<3s with some reagents.

31. Dabigatran
• TT linear concentration response to dabigatran
– most assays too sensitive
– high variability above 25ng/mL dabigatran
– sensitive method to determine if dabigatran present
• Normal TT excludes dabigatran
• Dabigatran quantitative assay
– Hemoclot thrombin inhibitor assay
– Essentially a diluted TT (1/8).
– Linear dose-response curve to 1000ng/mL.

32. Test Dabigatran Rivaroxaban Apixaban
PT Insensitive Sensitive Insensitive
APPT Sensitive Less sensitive Insensitive
TT V. Sensitive No effect No effect
Drug level Dilute TT Anti-Xa with
calibrator
Anti-Xa with
calibrator
Significant
anticoagulant
effect unlikely
TT and APTT
normal
PT normal (with
sensitive
thromboplastin)
Low drug level
Summary
But remember significant variability between assays.

33. Tran et al, New Oral Anticoagulants: a practical guide IMJ 44 (2014)

34. Tran et al, New Oral Anticoagulants: a practical guide IMJ 44 (2014)

35. Bleeding on DOA
• Same RF for bleeding as warfarin
• Increased bleeding from the GI system
• Higher risk in renal impairment
• Lower rate of ICH
• No specific antidote

36. ThrombosisBleeding
Problems of Haemostasis
Treat the problem
without
creating the opposite one
Somewhat more complicated of late?

37. Evidence for pro-
haemostatic agents
• Conflicting and limited
• No clinical trials in bleeding patients
– aPCC (FEIBA) and four factor PCC have been shown to reduce
bleeding in some animal models
• Variable effect on coag parameters in animals, healthy
volunteers and spiked plasma samples
– FEIBA more consistent impact on haemostatic changes
• unknown if this translates to superior clinical efficacy
– PCC (50IU/kg of 4 factor agent) reversed laboratory effects of
rivaroxaban, but not dabigatran
– rVIIa less consistent effect

38. Animal bleeding models
• Apparent dissociation between effect on lab tests and bleeding
tendency which is drug specific
• Mouse tail bleeding model
– Oral dabigatran = mean plasma level 200ng/mL
– PCC at 14.3ug/kg plus rFVIIa at 3mg/kg corrected the prolonged APTT but
did not reduce blood loss
• Rabbit kidney incision model with dabigatran
– Higher dose PCC up to 50ug/kg
– no effect on APTT
– increased thrombin generation in a dose-dependent manner
– reduced blood loss
• Rabbit hepato-splenic incision model
– 5mg/kg rivaroxaban
– treated before injury with 40ug/kg PCC or 150ug/kg rFVIIa.
– both partially corrected PT, APTT and ETP and rFVIIa corrected the
prolonged lag time
– neither reduced bleeding

39. Tran et al, New Oral Anticoagulants: a practical guide IMJ 44 (2014)

40. WATAG

43. Clot lysisClot formation
Thrombin Plasmin
Normal Haemostasis
Closely linked and carefully regulated processes
Correct calcium, hypothermia, acid-base balance

44. At present
• Opinion based recommendations
• Limited data for efficacy
• Off license use
• Potential thrombotic complications need to be balanced
– Guidelines for use in life threatening bleeding only
• Urgent measurement of the intensity of anticoagulation
to determine contribution of NOAC
• Recognize contributory coagulopathy unrelated to NOAC

45. Specific antidotes
• Dabigatran monoclonal antibody
– highly specific, rapid dose-dependent decrease in blood loss in
rat tail injury model, sustained for up to 6hrs and complete
reversal of anticoagulant effect on lab assays
• PRT4445
– universal reversal agent for Xa inhibitors.
– recombinant Xa that is haemostatically inactive and binds Xa
inhibitors
• Per977
– synthetic small molecule that binds NOACs
– reduced blood loss in rat tail injury model
– corrects aPTT and anti-Xa in ex vivo human blood

46. Other issues
• Identification of Rx failure
• Short T1/2 so measurement of the intensity of anticoagulation after the event will
not reliably discriminate treatment failure from inadequate anticoagulation v
inadequate compliance
• Drug monitoring
• Fixed dosing is effective and safe despite wide ranges for peak and trough
concentrations (ie wide therapeutic range)
– Group specific outcome of ODI patients in clinical trials is non-inferior to
warfarin. No published evidence base for monitoring and dose adjustment
for routine patients.
• Estimates that same dose of ODI can result in a 30% difference in thrombin
generation inhibition and therefore suggested thrombosis more likely in low
responders and bleeding more likely in high.
• Implication that dose adjustment would improve individual patient clinical
outcomes to be tested

47. Questions?

50. • Fixed dose group-specific outcomes:
– Assumed overall trial results generalisable to all patients in trial
and similar future patients
– Estimates that same dose of ODI can result in a 30% difference
in thrombin generation inhibition and therefore suggested
thrombosis more likely in low responders and bleeding more
likely in high.
– Implication that dose adjustment would improve individual
patient clinical outcomes has not been tested
– Group specific outcome of ODI patients in clinical trials is at least
non-inferior to warfarin, therefore monitoring and dose
adjustment for routine patients is not advisable until evidence
base for such a practice.

51. Test Thrombin
inhibitor
Clinical Utility Fxa inhibitors Clinical Utility
PT ++ No +++ Qualitative
APTT +++ Qualitative + Uncertain
TT ++++ Limited Not affected No
Dilute plasma
TT
+++ Quantitative Not affected No
Fibrinogen Not affected for
high thrombin
concentration
reagents
No Not affected No
D-dimer Not affected No Not affected No
RVVT ++ No ++ No
Chromogenic
anti Xa
Not affected No +++ Quantitative
Clotting factors False low with
clot-based
assays.
Positive
Testing not
recommended
False low with
clot-based
assays.
Positive
Testing not
recommended

52. Dabigatran experience
• RE-LY trial
– Both doses of dabigatran had lower risks of intra and extra cranial
bleeding cg warfarin in those <75years
– Patients >75 years had lower risk of ICH, but similar or higher rate of
extracranial bleeds that warfarin
– Added single anti-platelet agent inceased major bleeding risk HR 1.6
– Dual antiplatelet therapy HR 2.31
– Post marketing reports on dabigatran for AF report similar bleeding
rates as the phase III trial
ASH abstract 2012: post hoc analysis of major bleeding from 5 pahse III
trails
lower 30 day mortality with dabigatran that warfarin
most patients with major bleeding treated with supportive measures only
without factor concentrates.

53. GI bleeding
• Rivaroxaban and dabigatran 1.5 fold increased risk GI
bleeding cf warfarin
• Mechanism possibly incomplete absorption and local
effects on gut mucosa rather than systemic
anticoagulation effect as with warfarin.
• Apixaban has less GI bleeding
– Possibly as more frequent dosing so reduced peak.

54. Hillarp, A et al. Journal of Thrombosis and haemostasis, 12: 1-9

55. Coagulation: Step 1:
Initiation
• Initiation of clotting occurs
when disruption of the
endothelium exposes activated
factor VII (VIIa) in blood to
tissue factor on subendothelial
cells (smooth muscle cells and
fibroblasts)
• FVIIa-TF complex activates
other clotting proteins (esp. FX
and FIX)
• Small amount of thrombin is
formed

56. Coagulation: Step 2:
Propagation
• Thrombin (IIa) activates
platelets which release further
coagulation proteins
• Thrombin activates
coagulation proteins required
for its own production
• Large scale production of
thrombin takes place on
platelet surface

57. Summary of haemostasis after
disruption of vascular
endothelium
• Platelets bind to subendothelial collagen to initiate primary closure
of the vessel wall defect
• Tissue factor in subendothelium combines with FVII in blood to form
the FVIIa-TF complex
• FVIIa-TF complex activates other clotting proteins leading to
thrombin production
• Large scale production of thrombin takes place on the platelet
surface
• Thrombin converts fibrinogen to fibrin
• Fibrinolysis is activated to localise the clot to the site of injury

58. Dagibatran etexilate (Pradaxa)
• Prodrug of dabigatran
• Low oral bioavailability
– Breaking the capsule can significantly increase bioavailability
– Food does not effect bioavailability but take with food to minimise
dyspepsia
• Until metabolised to dabigatran, is a substrate for P-glycoprotein
efflux transporter
– interacts with drugs that induce this pathway.
• Binds thrombin active site and blocks free and clot bound thrombin.
• Predominantly renal excretion
– Contraindicated if CrCl <30ml/min
• If dose missed, take within 6 hours or omit if >6hours have elapsed.

59. Rivaroxaban
• Inactivates free and clot-associated factor Xa
• OD dosing, bioavailability 80%, 90% protein bound
– Oral absorption excellent for 10mg does but higher doses taken
with food to improve bioavailability
• Predominantly eliminated by liver
• No accumulation of drug when CrCl >15ml/min but dose
reduction to 15mg OD if CrCl 15-30ml/min
• Kinetics effected by drugs that affect P-glycoprotein and
cytochrome P45o3A4, but not CYP2C9
• If dose missed take next dose within 12 hours but does
omitted if >6hrs elapsed

60. Apixaban
• Bioavailability 50%
• Extremes of body weight effect bioavailability
• Metabolised through liver
• Does not accumulate in mild-moderate renal impairment
• CYP3A4 metabolism and P-glycoprotein substrate

62. • Meta-analysis in AF
– Trend toward reduced major bleeding (RR 0.86)
– Significant reduction in ICH compared to warfarin (RR0.46)
– Major GI bleeding more common with dabigatran and
rivaroxaban than warfarin
• Meta-analysis in VTE
– Rivaroxaban reduced the risk of major bleeding compared with
warfarin
– Other DOA did not