5: Anti-platelet, anticoagulant and thrombolytic drugs Flashcards
What is haemostasis?
Arrest of blood loss from a damaged vessel
(stopping bleeding)
What is the sequence of events of haemostasis?
Vasodilation at site of injury
Platelets arrive at site of injury
Formation of fibrin (blood coagulation)
What is exposed when a vascular wall is damaged?
Collagen
Tissue factor (receptor)
Which protein helps with the adhesion, activation and aggregation of platelets to damaged blood vessels?
Fibrinogen
When fibrinogen triggers the aggregation of platelets, what forms in the blood vessel?
Soft plug
What is fibrinogen converted into during coagulation?
Fibrin
What is thrombosis?
Pathological haemostasis i.e a clot forms without prior bleeding
Virchow’s triad shows the predisposing factors for ___.
thrombosis
What are the three prothrombotic factors of Virchow’s triad?
Injury to vessel wall
Abnormal blood flow
Increased coagulability of blood
An arterial thrombus is also known as a ___ thrombus.
white
What does a white thrombus consist of?
Platelets in a fibrin mesh
When a white thrombus detaches from its site of origin, it may form an ___.
embolus
Which drugs are used to treat white thrombi?
ANTIPLATELET DRUGS
A venous thrombus is also known as a ___ thrombus.
red
Which drugs are used to treat red thrombi?
ANTICOAGULANT DRUGS
Where do emboli from white thrombi usually lodge?
Coronary arteries
Carotids
Subarachnoid
Where do emboli from red thrombi usually lodge?
Pulmonary arteries
(PE)
Which drug blocks modification of factors X and II?
Warfarin
What drug directly inhibits activated factor X (Xa)?
Rivaroxiban
Which drugs indirectly block activated factor X (Xa)?
Heparins
Fondaparinux
Which drug directly inactivates activated factor II (IIa), which is responsible for thrombin production?
Dabigatran
(Heparin also does, indirectly)
___ factors act as precursors for ___ factors.
inactive , active
Which sort of enzyme do inactive precursor factors act as?
Serine proteases
Which process do precursor factors undergo to become active factors?
gamma carboxylation
What is required for gamma carboxylation of inactive precursor factors to active factors?
Vitamin K
Which enzyme, important in gamma carboxylation of inactive precursor factors, does warfarin act on?
Vitamin K reductase
What acts (with a delay) on vitamin K reductase to bring about an anticogulative effect?
Warfarin
How long does it take for warfarin to produce an anticoagulative effect?
2-3 days
Which type of thrombosis are anticoagulants used to treat?
Venous / red thrombosis
Give an example of a case where an anticoagulant drug would be used to prevent venous thrombosis and embolism.
DVT
Post-surgery
Artificial heart valves
Atrial fibrillation
What is a significant risk when using anticoagulative drugs like warfarin?
Haemorrhage
How is warfarin administered?
Oral
Which drug produces a rapid anticoagulant effect?
Heparin (or a LMWH)
How many half-lives would you clear a drug (e.g heparin) for before commencing a procedure which required its absence?
5 half-lives (200 hrs in case of warfarin)
What property of warfarin makes it difficult to strike a balance between desired anticoagulant effect and haemorrhage?
Low therapeutic index
Which factors increase the risk of haemorrhage when using warfarin?
Liver disease
High metabolic rate (hyperthyroidism?)
Loads of drug interactions
Which factors increase the risk of thrombosis when using warfarin?
Pregnancy
Hypothyroidism
Vitamin K consumption
Loads of drug interactions
If someone took too much warfarin and haemorrhaged, what would you give them?
Vitamin K
plasma clotting factors
What does antithrombin III resist the effect of?
Thrombin
What process does antithrombin III inhibit?
Coagulation
Which drug binds to antithrombin III to increase its effect?
Heparin
Which factors does antithrombin III act on to produce an anticoagulative effect?
Xa and IIa
Name a low molecular weight heparin (LMWH).
Dalteparin
Enoxaparin
Fondaparinux
Idrabiotaparinux
LMWHs act on antithrombin III to inhibit activated factor __.
Xa
How is heparin administered?
IV (immediate onset)
Subcutaneously (works within an hour)
Heparin is the preferred anticoagulant in which type of organ failure?
Renal failure
Name two other anticoagulative drugs (other than warfarin and heparin).
Dabigatran
Rivaroxaban
Which drug blocks ADP channels on platelets?
Clopidogrel
Which drug blocks COX-1? lol
Aspirin
