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PR3154 > IC3 Anticoagulants > Flashcards

IC3 Anticoagulants Flashcards

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1
Q

Which step of hemostasis do Anticoagulants block?

A
  • Secondary hemostasis
  • Block activation of fibrin polymerization by preventing conversion of fibrinogen to fibrin
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2
Q

List & classify the Anticoagulants according to their route of administration

A

Oral
Warfarin
Dabigatran
Rivaroxaban

Parenteral
Heparin
LMWHs

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3
Q

Which oral Anticoagulants are antagonists of Vitamin K & which are not?

A

Vitamin K Antagonist
Warfarin

Non-Vitamin K Antagonist
Dabigatran
Rivaroxaban

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4
Q

What is the MOA of Warfarin?

A
  • Active Vitamin K = reduced form
  • Inactive Vitamin K = oxidised form
  • Active Vitamin K is oxidised to inactive Vitamin K in a step that is coupled to the carboxylation of glutamic acid residues (on coagulation factors II, VII, IX & X)
  • Carboxylation activates the factors II, VII, IX & X
  • Warfarin inhibits Vitamin K reductase, the enzyme that reactivates the oxidized Vitamin K → Prevents activation of clotting factors
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5
Q

What is the reversal agent for Warfarin?

A

Vitamin K

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6
Q

What is the onset, time to peak plasma concentration & duration of action of Warfarin?

A

Onset
24 to 72h for oral, effects kick in when endogenous reserves of active vitamin K are depleted

Time to peak, plasma
2 to 8h for oral

Duration of action
2 to 5 days

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7
Q

How long is needed before full therapeutic effect can be achieved for Warfarin? Suggest why

A
  • 5 to 7 days
  • As some of the coagulation factors have a long half-life
    e.g. Factor II (prothrombin) has T1/2 = 50 h
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8
Q

How well absorbed is Warfarin & how is it excreted?

A

Absorption
Rapid & complete oral absorption

Excretion
Urine & faeces

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9
Q

How is Warfarin metabolised & what is its half life elimination?

A
  • Metabolised by liver, primarily via CYP2C9
  • Half-life elimination is 20-60 hours, highly variable among individuals
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10
Q

Why does Warfarin have a variable response?

A
  • Mostly due to genetic polymorphisms in 2 genes
    CYP2C9 & Vit K reductase complex, subunit 1 or VKORC1
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11
Q

What are the 2 main parameters used to monitor & titrate Warfarin dose?

A
  • International normalized ratio (INR)
  • Prothrombin time (PT)
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12
Q

What is a common adverse effect of Warfarin?

A

Haemorrhage / bleeding 🩸
Signs include blood in stools or urine, melaena (sticky, tar-like stools), excessive bruising, petechiae, persistent oozing from superficial injuries, excessive menstrual bleeding

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13
Q

What are the rare adverse effects of Warfarin? State the risk factors if any

A

Hepatitis
Greatest risk if >60 y/o, male, on warfarin < 1 month

Cutaneous necrosis & infarction of breast, buttocks and extremities
Likely due to ↓ blood supply to adipose tissue
Typically occurs 3 to 5 days after initiation

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14
Q

What are the contraindications of Warfarin?

A
  • Hypersensitivity to drug
  • Bleeding associated: Active bleeding, risk of pathologic bleeding, after recent major surgery
  • Severe or malignant hypertension
  • Severe renal or hepatic disease
  • Subacute bacterial endocarditis, pericarditis, or pericardial effusion
  • Pregnancy (teratogenic: severe defects in bone & CNS, can cause haemorrhagic disorder in fetus)
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15
Q

In whom should cautions be taken for Warfarin?

A
  • Breast-feeding women
  • Diverticulitis, colitis
  • Mild or moderate hypertension
  • Mild or moderate renal / hepatic disease
  • Drainage tubes in any orifice
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16
Q

What are the drugs that may increase bleeding risks when used concomitantly with Warfarin?

A
  • Paracetamol (warn patients! can get OTC easily)
    when used long term (>2 weeks) at high doses (> 2g/day)
  • CYP2C9 inhibitors (allopurinol, NSAIDs, salicylates, PPI, metronidazole)
  • Other antiplatelets or anticoagulants
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17
Q

What are the traditional medicines/herbs/supplements/food that may increase bleeding risks when used concomitantly with Warfarin?

Study These Flashcards
A
  • Gingko 🍁
  • Ginseng
  • Reishi mushrooms 🍄
  • Cranberry juice
18
Q

What drugs may reduce the efficacy of Warfarin when used concomitantly?

Study These Flashcards
A

CYP2C9 inducers
* Barbiturates
* Corticosteroids
* Spironolactone, thiazide (diuretics)

19
Q

What are the traditional medicines/herbs/supplements/food that may reduce the efficacy of Warfarin when used concomitantly?

Study These Flashcards
A
  • Vitamin K containing supplements
  • Vitamin K-rich foods (mustard greens, spinach)
    Ask patients to avoid excess vitamin K intake
  • Green tea
20
Q

What should we monitor for drug-drug or drug-food interactions that may reduce efficacy of Warfarin?

Study These Flashcards
A

Regular INR monitoring to ensure appropriate anticoagulant control

21
Q

Which DOAC is a prodrug?

Study These Flashcards
A

Dabigatran etexilate
rapidly converted to dabigatran

22
Q

What is the difference between the target(s) of Dabigatran vs Rivaroxaban?

Study These Flashcards
A
  • Dabigatran & its acyl glucuronide metabolites are competitive reversible non-peptide antagonists of thrombin (factor IIa) while
  • Rivaroxaban is a competitive reversible antagonist of activated factor X (Xa)
23
Q

Which drug is Idarucizumab used as a reversal agent? Explain what it is & when it is indicated

Study These Flashcards
A
  • Dabigatran
  • Is a humanized mAb fragment that binds Dabigatran & its acyl glucuronide metabolites with higher affinity than Dabigatran to thrombin
  • Indicated for
    1. Emergency surgery or urgent procedures
    2. Life-threatening or uncontrolled bleeding
24
Q

Which drug is 🥨 Andexanet alfa used as a reversal agent? Explain what it is

Study These Flashcards
A
  • Rivaroxaban or other -xabans
  • Off-label for LMWHs
  • Is a recombinant modified human factor Xa decoy protein
25
What are the advantages of DOACs over Warfarin?
* Less drug, food interactions * Less interindividual variability But DOACs are more expensive
26
Does Dabigatran etexilate or Rivaroxaban take a shorter time for reversal?
* Rivaroxaban * Takes 1-2 days as half life is shorter, at 5 to 9h * vs Dabigatran etexilate whose reversal takes 3-5 days as half life is longer, at 12 to 17h
27
Compare the adverse effects of Dabigatran etexilate & Rivaroxaban
* Both may cause bleeding * Dabigatran etexilate may also cause GI symptoms
28
Does Dabigatran etexilate or Rivaroxaban have better bioavailability?
* Rivaroxaban (80 to 100%) * Dabigatran etexilate (3 to 7%...so administered as enteric coated formulation)
29
Compare the drugs that increase bleeding risks of Dabigatran etexilate & Rivaroxaban
**Dabigatran etexilate** Antiplatelets, anticoagulants, NSAIDs, fibrinolytics & ketoconazole **Rivaroxaban** Antiplatelets, anticoagulants, NSAIDs, P-gp & CYP3A4 **inhibitors**
30
Compare the respective drugs that reduce the levels of Dabigatran etexilate & Rivaroxaban
**Dabigatran etexilate** RifamPIn **Rivaroxaban** P-gp & CYP3A4 **inducers**
31
What is the MOA of Heparin & LMWHs?
* Potentiate the action of antithrombin III (AT III), thereby inactivating thrombin * Thrombin is needed for conversion of fibrinogen to fibrin * Without fibrin, clot formation is impeded * Active heparin molecules bind tightly to AT III → cause a conformational change which exposes AT III’s active site for more rapid interaction with proteases → accelerate inactivation of coagulation factors
32
What are the factors inactivated by Heparin vs LMWHs?
**Heparin** 🥨 **Heparin-AT III complex** **inactivates thrombin (Factor IIa)**, IXa, 🥨 **Xa**, XIa & XIIa **LMWHs e.g. enoxaparin** 🥨 **Factor Xa** & to a lesser extent, IIa
33
Which parenteral anticoagulant is good at blocking surface contact triggered coagulation?
* Heparins (not LMWHs) * Also used in tubes for blood samples
34
What are the features of LMWHs that make them favourable over Heparin?
1. Longer half-life (4h vs 1h) 2. Higher bioavailability (86 to 98% vs 30%) 3. Less need for INR monitoring as response is more consistent 4. Lower risk of heparin-induced thrombocytopenia
35
Parenteral anticoagulants are administered _______
IV, subcutaneously
36
How is LMWHs vs Heparin excreted?
LMWHs are excreted renally but Heparins are via nonrenal mechanisms
37
What are the adverse effects of parenteral anticoagulants?
**1. Bleeding** (in 1-5 % of patients treated with IV heparin) Anticoagulant effect **disappears within hours of discontinuation** **2. ↑ Risk of epidural or spinal haematoma & paralysis** in patients receiving epidural, spinal anaesthesia or spinal puncture **3. Heparin-induced thrombocytopenia** Binds to platelet factor 4 (PF4) on activated platelet surface, triggering formation of IgG antibody against the heparin-PF4 complex Even after discontinuation, antibodies sometimes continue to attack platelets (Lower risk with LMWHs)
38
How can effects of parenteral anticoagulants be reversed?
* IV infusion of 🥨 **Protamine sulfate** * Mainly for heparin, incomplete reversal if used for LMWHs * Is a highly basic peptide that binds stably to negatively charged heparin → neutralise anticoagulant properties of heparin
39
Are parenteral anticoagulants safe for use in pregnancy?
* Both Heparin & LMWH do not cross the placenta (unlike Warfarin) * Not been a/w fetal malformations
40
What are the contraindications for parenteral anticoagulants?
* Hypersensitive to heparins or pork products (those hypersensitive to pork showed cross reactivity to heparins) * Active major bleeding * Thrombocytopenia or antiplatelet antibodies
41
In whom should caution be exercised for parenteral anticoagulants?
* Elderly patients * Risk of bleeding Including patients with prosthetic heart valves, major surgery, regional or lumbar block anaesthesia, blood dyscrasias, recent childbirth, pericarditis or pericardial effusion & (LMWHs) renal insufficiency
42
What are the drug/food/herb interactions with parenteral anticoagulants?
**All ↑ risk of bleeding** **Drugs** Antiplatelets, anticoagulants, fibrinolytics, NSAIDs, **SSRIs** **Herbs/foods** Chamomile, fenugreek, garlic, ginger, ginkgo & ginseng

PR3154 (3 decks)

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