New Oral Anticoagulants

NOACs

Dr Carolyn Grove

Clinical and Laboratory Haematologist

Sir Charles Gairdner Hospital and

PathWest Laboratory Medicine

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

Coagulation Cascade

PL – Platelet Membrane PhospholipidTF - 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

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

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

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

Case 1: Discussion Points

• What does the rivaroxaban level mean?

• Is this a typical picture for coagulation parameters on therapeutic rivaroxaban?

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)

PTAPTT

Tests: PT and APTT

Principles….Citrated bloodCentrifuged -> Platelet poor plasma

+ Activator + Platelet substitute + Calcium ->Measure time to clot formation

Rivaroxaban and Coags

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

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

Ex vivo experiment with rivaroxaban (10 mg)

Asmis, L.M. et al Thrombosis Research 129 (2012) 492-498

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

Case 2

78 y.o. man

A&E

0-1

D/C

Coronary angiography

and drug eluting stentTicagrelor +

aspirin

-40 -8

Right upper lobectomy and wedge lower lobe resection

-7

AF+ HD instability

-5

Chest painNo new

changes on angiogram

-4

Start apixaban 5mg bd

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

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

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?

Apixaban Levels

10mg single dose fasted v fed

Frost C et al. Br J Clin Pharmacol. 2013 Feb;75(2):476-87

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

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.

Apixaban concentration to

double APTT

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

Apixaban and INR

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

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

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

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

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?

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

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

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

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.

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.

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.

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

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

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

ThrombosisBleeding

Problems of Haemostasis

Treat the problem

without

creating the opposite one

Somewhat more complicated of late?

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

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

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

WATAG

Clot lysisClot formation

Thrombin Plasmin

Normal Haemostasis

Closely linked and carefully regulated processes

Correct calcium, hypothermia, acid-base balance

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

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

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

Questions?

• 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.

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 inhibitor screen and Bethesda

Testing not recommended

False low with clot-based assays. Positive inhibitor screen and Bethesda

Testing not recommended

Antithrombin Fxa inhibition assay not affected

FIIa inhibition assay not affected

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 trailslower 30 day mortality with dabigatran that warfarinmost patients with major bleeding treated with supportive measures only without factor concentrates.

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.

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

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

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

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

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.

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

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

• 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