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MD2002 > Anticoagulant Drugs > Flashcards

Anticoagulant Drugs Flashcards

1
Q

What is haemostasis ?

A

The arrest of blood loss from damaged blood vessels

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2
Q

What are the main ways in which haemostasis occurs.

A
  • Vascularconstriction
  • Formation of a platelet plug
  • Formation of a blood clot as a result of blood coagulation
  • Growth of fibrous tissue into the blood clot to close the hole permanently
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3
Q

Is promotion of haemostasis ever necessary ? Using what drug ?

A

Rarely, using tranexamic acid

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4
Q

Which steps of thrombosis does drug therapy target ?

A
  • Blood clotting
  • Platelet adhesion and activation
  • Processes involved in fibrin removal
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5
Q

Identify an example of condition due to genetically determined deficiencies of clotting factors. How is this condition treated ?

A

Haemophilia

Treated with replacement therapy

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6
Q

What are possible causes of acquired clotting defects ? How are these treated ?

A

Liver Disease
Vitamin K deficiency
Ingestion of oral anti-coagulants

Treated with

  1. natural Vitamin K (phytomenadione) or
  2. synthetic preparation, menadiol sodium phosphate
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7
Q

What is the role of vitamin K in the treatment of clotting defects ?

A

Acts as co-factor for “the gamma-carboxylase enzymes which catalyze the posttranslational gamma-carboxylation of glutamic acid residues in inactive hepatic precursors of coagulation factors II (prothrombin), VII, IX and X”

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8
Q

What are all the clinical uses of vitamin K ?

A
  • Treatment and/or prevention of bleeding from excessive oral anticoagulant use
  • In babies to prevent haemorrhagic disease of the newborn
  • For Vitamin K deficiencies in adults
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9
Q

Identify antagonists of vitamin K.

A

Warfarin

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10
Q

How does warfarin inhibit vitamin K action ?

A

Prevents reduction of vitamin K

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11
Q

What is the onset of warfarin ? Why ?

A

Takes many hours to act because of time taken for degradation of factors

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12
Q

How may one cover for the slow onset of warfarin ?

A

Using heparin treatment

Giving loading dose of warfarin then go down to small dose to try and maintain plasma levels

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13
Q

What is the main side effect of warfarin ? How can this be treated ?

A

haemorrhage

Can be reversed by Vitamin K

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14
Q

How are patients’ response to the dose of warfarin measured ?

A

Prothrombin Time test, allows to calculate International Normalized Ratio (INR)

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15
Q

Identify factors which increase the effect of warfarin.

A
  • ↓ availability of Vitamin K
  • Broad-spectrum antibiotics
  • Liver disease
  • Drugs which:
  • impair platelet function
  • displace warfarin from their binding sites on plasma albumin
  • agents which inhibit microsomal enzymes in the liver

-Dietary factors

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16
Q

Identify factors which decrease the effect of warfarin.

A
  • Drugs which ↑ drug metabolism
  • Oral contraceptives
  • Dietary factors
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17
Q

What is the method of administration of warfarin ?

A

Orally

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18
Q

What is the method of administration of heparin ?

A

Injected

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19
Q

Give an example of heparin.

A

Dalteparin

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20
Q

What kind of molecule are heparins ?

A

sulphated glycosaminoglycans

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21
Q

What are the main two groups of heparin ? What is their main distinction ?

A

Unfractionated (UFH) or Low Molecular Weight (LMWH)

LMWH longer acting, don’t require monitoring

22
Q

Where is heparin found in the body ?

A

In mast cells, in plasma and in endothelial cells

23
Q

What is the onset of heparin ?

A

Starts acting almost immediately

24
Q

What is the main side effect of heparin ?

How can this be treated ?

A

Haemorrhage

May be reversed by protamine

25
Q

What is the mechanism of action of heparin ?

A
  • Antithrombin forms a 1:1 complex with thrombin by binding to active site, thus inhibiting thrombin
  • Heparin acts on antithrombin III (naturally-occurring inhibitor of thrombin) and other serine proteases in the coagulation cascade (XIIa, XIa, IXa, & Xa) (brings ATIII to activated factors)
  • As a result, heparin accelerates the rate of this inhibition (thus prevents fibrin formation)
26
Q

Which chemical property of heparin relates to its mechanism of action in preventing blood clotting ?

A

Electronegative charge

27
Q

Identify two direct factor Xa inhibitors ?

A

Rivaroxaban or apixaban

28
Q

What is the route of adminsitration of direct factor Xa inhibitors ?

29
Q

How is response to direct factor Xa inhibitors measured ?

A

Does not require PT/INR monitoring (Meaningless for these drugs!)

30
Q

What is the onset of direct factor Xa inhibitors ?

A

Rapid onset of action compared to warfarin, just takes a few hour

31
Q

What is the duration of effect of direct factor Xa inhibitors ? How long does it take before factor Xa normal activity comes back to normal ?

A

8-12 hours

24 hours

32
Q

What is the main side effect of direct factor Xa inhibitors ? How is this treated

A

Haemorrhage

No antidote

33
Q

Are anti-platelets and anti-coagulants the same ?

34
Q

Identify two examples of anti-platelet drugs.

A

Aspirin

Clopidogrel

35
Q

How do aspirin and Clopidogrel respectively inhibit platelet

A

ASPIRIN
Inhibits cyclooxegenase
Stops production of thromboxanes which would normally increase expression of receptors that lead to aggregation

CLOPIDOGREL
Inhibits P2Y12 purinergic receptors
Inhibits ADP-induced platelet aggregation

36
Q

What is the general function of Antiplatelet drugs ?

A

Decrease platelet aggregation and thereby inhibit thrombus formation

37
Q

What is Fibrinolysis ?

A

Breaking down of thrombus

38
Q

When is fibrinolysis induced ?

A

When the intrinsic coagulation system is activated

39
Q

Describe the mechanism of fibrinolysis.

A
  • Generation of plasminogen activators
  • Plasminogen activators release active enzyme plasmin from plasminogen precursor
  • Plasmin digests not only fibrin but other blood proteins such as factors II, V & VII
40
Q

What is plasminogen ?

A

Inactive pro-enzyme deposited in the fibrin strands within a thrombus

41
Q

What is plasmin ?

A

Trypsin-like enzyme acting on ARG-LYS bonds

42
Q

How is plasmin which escapes into circulation removed after having fulfilled its function ?

A

Plasmin which escapes into the circulation is inactivated by various plasmin inhibitors

43
Q

Give examples of fibrinolytic agents.

A

Streptokinase, Alteplase

44
Q

What kind of organic molecule is streptokinase ?

A

Non-enzymatic protein

45
Q

How does streptokinase lead to fibrinolysis ?

A

Acts indirectly by forming a stable complex with plasminogen. This activates enzymatic activity of plasminogen by inducing a conformational change.

46
Q

Give an example of Tissue Plasminogen Activator. How is this plasminogen activator synthesised ?

A

ALTEPLASE

Synthesised in vivo by endothelial cells, but can also be made by recombinant technology

47
Q

How is Alteplase clot selective (does not just activate plasminogen in the plasma) ?

A

Because Alteplase’s enzymatic activity is enhanced more in the presence of fibrin-bound plasminogen than plasma plasminogen

48
Q

Overall, what are the main groups of drugs which target thrombosis ? What process does each of these inhibit/activate ?

A
  1. Anticoagulants (Heparin, Warfarin, Factor Xa inhibitors): Inhibits activation of clotting factors (XIIa, IXa, XIa, Xa)
  2. Antiplatelet agents (Aspirin, Clopidogrel): Inhibits platelet adhesion, activation, aggregation
  3. Fibrinolytic agents (Streptokinase, Alteplase): Enhances conversion of Plasminogen into Plasmin (which digests fibrin and blood proteins)
49
Q

What are some therapeutic uses of anticoagulants ?

A

VENOUS THROMBOEMBOLISM

TREATMENT AND PROPHYLAXIS OF
– DVT
– Pulmonary embolisms
– Thromboembolism from atrial fibrillation 
– Prosthetic heart valves
– Clotting during kidney dialysis
50
Q

What specific anticoagulants are given for venous thromboembolisms ?

A

– Heparin for short-tem action

– Oral anticoagulants for prolonged therapy

51
Q

What are some therapeutic uses of antiplatelet agents and fibrinolytic agents ?

A

FIBRINOLYTIC AGENTS + ASPIRIN
-therapy of acute myocardial infaraction (within 4-6 hours of onset)

ASPIRIN
-can reduce the risk of occlusive cardiovascular disease in patients already diagnosed as being at risk

MD2002 (108 decks)

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