Anticoagulants, drugs affecting blood clotting Flashcards
What do anticoagulants do
They interfere with or block soem aspect of blood coagulation
How can anticoagulants be classified
As oral or injectable
Give examples of anticoagulants
- Heparin
- Warfarin
- Phenindione
What is the principle mode of action of heparin
Action on antithrombin III
This inhibits thrombin and inactivates prothrombin
Anti thrombin III neutralises several of the activated clotting factors
Heparin activates antithrombin and accelerates its rate of action
How is heparin given
Either intravenously or subcutaneously
Where is heparin metabolised
Liver and excreted via kidneys
When does an intravenous injection of heparin begin to work
Immediately
When does a subcutaneous injection of heparin begin to work
50-60 mins after dosing
List some unwanted side effects associated with heparin
Haemorrhage most commonly from the gastrointestinal or genitourinary tract
What should we do if a patent on heparin suffers form haemorrhage
Stop administrating heparin and give the patietn protamine sulphate 1mg for every 100 units of heparin
How does warfarin work
It acts as an antagonist to the vitamin K dependent clotting factors (eg II, VII, IX, X)
When is low molecular weight heparin used clinically
When there is an immediate need for anticoagulation eg DVT and pulmonary embolism
When is warfarin given to patients
Used in the prophylaxis of embolisation in rheumatic heart disease, heart valve replacement and atrial fibrillation
also used in the management of DVT and pulmonary emboloism where 3-6 month course is given after initial heparin treatment
What do Antiplatelet drugs do
They decrease platelet aggregation and may also inhibit thrombus formation in the arterial circulation where anticoagulants have little or no effect
Give examples of Antiplatelet drugs
- Aspirin
- Clopidogrel
- Dipyridamole
What does aspirin do
Increase bleeding time by reducing platelet aggregation
How does aspirin work
It inhibits the synthesis of thromboxane A2 in the platelet by blocking cyclo-oxygenase
What is thromboxane A2
A prostaglandin that promotes platelet aggregation
How long can the effect of a single dose of aspirin last
7-10 days
When is aspirin given
- 150-300 mg is given soon as possible after an ischaemic even
- 75mg is used for long term maintenance or prophylaxis of established cardiovascular disease
What does clopidogrel do
Inhibits ADP induced platelet aggregation and is often used in combination with aspirin in the prevention of atherosclerotic events
What is dipyridamole
is a phosphodiesterase inhibitor with an antithrombotic effect based upon its ability to modify various aspects of platelet function such as adhesion, aggregation and survival.
What is the main use of Dipyridamole
Used as an adjunct to oral anticoagulants for the prophylaxis of thromboembolism associated with prosthetic heart valves and as an adjunct to aspirin following a stroke or transient ischaemic attack
What do fibrinolytic drugs do
Promotes the breakdown of thrombi by activating plasminogen to form plasmin
Give examples of fibrinolytic drugs
- alteplase
- streptokinase,
- reteplase
- tenacteplase.
When are fibrinolytic drugs indicated
Acute mI and other life threatening thromboembolic disorders
What is alteplase
A tissue plasminogen activator which acrivats bound plasminogens
When is alteplase used
Managements of acute MI and pulmonary embolism
What is the main unwanted effect of alteplase
haemorrhage
what is Streptokinase
it is a protein derived from β-haemolytic streptococci, which interacts with the proactivator of plasminogen to catalyse the conversion of plasminogen to plasmin
What do Antifibrinolytic drugs do
Encourage the stabilisation of fibrin by inhibiting plasminogen activation
Name the most commonly used Antifibrinolytic drug in dentistry
tranexamic acid,
When is tranexamic acid given to patients
Used as a mouthwash in controlling persistent haemorrhage after tooth extraction.
