Oral anticoagulants

Question 1

why are anticoagulants prescribed?

Answer 1

To prevent thrombus formation or extension of an existing thrombus in the slower-moving venous side of the circulation, where the thrombus consists of a fibrin web enmeshed with platelets and red cells

Question 2

why are anticoagulants of less use in preventing thrombus formation in arteries?

Answer 2

In faster-flowing vessels thrombi are composed mainly of platelets with little fibrin

Question 3

The oral anticoagulants warfarin, acenocoumarol and phenindione, antagonise the effects of vitamin K. How long does it take for the anticoagulant effects to develop fully with these drugs?

Answer 3

At least 48 to 72 hours for the anticoagulant effect to develop fully (warfarin is the drug of choice)

Question 4

Because it can take oral anticoagulants at least 48 to 72 hours to start workin, what can be given if immediate anticoagulation is required?

Answer 4

unfractionated or low molecular weight heparin can be given concomitantly

Question 5

why should oral anticoagulants not be used in cerebral artery thrombosis or peripheral artery occlusion as first-line therapy?

Answer 5

aspirin is more appropriate for reduction of risk in transient ischaemic attacks

Question 6

which anticoagulant is usually preferred for the prophylaxis of venous thromboembolism in patients undergoing surgery?

Answer 6

1) Unfractionated or a low molecular weight heparin
2) alternatively, warfarin can be continued in patients currently taking long-term warfarin and who are at high risk of thromboembolism

Question 7

How is the dose of oral anticoagulants be determined?

Answer 7

The base-line prothrombin time should be determine as this is what the dose is based on. the initial dose should not be delayed whilst awaiting the result.

Question 8

An INR which is within how many units of the target value is generally satisfactory?

Answer 8

1) An INR which is within 0.5 units of the target value is generally satisfactory
↳ Target values (rather than ranges) are now recommended.

Question 9

An INR of 2.5 in those taking warfarin is indicated for which conditions?

Answer 9

1) Treatment of DVT and PE
2) Cardioversion
3) myocardial infarction
4) bioprosthetic heart valves
etc

Question 10

An INR of 3.5 in those taking warfarin is indicated for which conditions?

Answer 10

Recurrent DVT or PE in patients currently receiving anticoagulation and with an INR above 2

Question 11

For the following, state the recommended duration of anticoagulation with warfarin:

1) Isolated calf-vein DVT
2) VTE provoked by surgery
3) unprovoked proximal DVT or PE

Answer 11

1) Isolated calf-vein DVT: 6 weeks
2) VTE provoked by surgery or other transient risk factor (e.g. COC use, pregnancy, plaster cast): 3 months
3) unprovoked proximal DVT or PE: at least 3 months; long-term anticoagulation may be required.

Question 12

The main adverse effect of all oral anticoagulants is haemorrhage. Checking the INR and omitting doses when appropriate is essential. If the anticoagulant is stopped but not reversed how many days later should the INR be rechecked?

Answer 12

INR should be measured 2–3 days later to ensure that it is falling. Investigate cause as well

Question 13

Outline the treatment of major bleeding in those taking warfarin

Answer 13

1) Stop warfarin and give phytomenadione (vit K1) by slow IV injection
2) Give dried prothrombin complex, (if unavailable, fresh frozen plasma can be given but is less effective)

Question 14

1) How would you manage a patient with an INR of >8.0 presenting with minor bleeding?
2) when would the warfarin be restarted?

Answer 14

1) Stop warfarin and give phytomenadione by slow IV injection. Repeat dose of phytomenadione if INR still too high after 24 hours
2) Restart warfarin when INR <5.0

Question 15

How would you manage a patient with an INR of >8.0 presenting with no bleeding

Answer 15

1) Stop warfarin and give phytomenadione by mouth using the IV preparation orally [unlic]. Repeat dose of phytomenadione if INR still too high after 24 hours
2) Restart warfarin when INR <5.0

Question 16

how would you manage the following INR results in patients taking warfarin:

1) INR 5.0–8.0, minor bleeding
2) INR 5.0–8.0, no bleeding

Answer 16

1) 5-8 Minor bleeding : Stop warfarin, give phytomenadione by slow IV injection; restart warfarin sodium when INR <5.0
2) 5-8 No bleeding: Withhold 1 or 2 doses of warfarin and reduce subsequent maintenance dose

Question 17

what is the INR level in normal healthy people?

Answer 17

INR of 1.1 or below is considered normal

Question 18

1) How many days before elective surgery is warfarin usually stopped?
2) An INR of < 1.5 is the goal for most procedures. What should be done if it is still above this level after stopping warfarin?
3) when can warfarin be resumed following surgery?

Answer 18

1) 5 days before elective surgery
2) Phytomenadione by mouth [unl] given the day before surgery if the INR is ≥1.5
3) Resumed at the normal dose on the evening of surgery or the next day

Question 19

Outline how patients stopping warfarin prior to surgery, who are considered to be at high risk of thromboembolism should be managed?

Answer 19

1) Interim therapy (‘bridging’) with a LMWH (using treatment dose)
2) Stopped LMWH at least 24 hours before surgery
3) If the surgery carries a high risk of bleeding, the LMWH started 48 hours after surgery

Question 20

How should the following patients on warfarin be managed?

1) Emergency surgery that can be delayed for 6-12 hours
2) If surgery cannot be delayed

Answer 20

1) Can be delayed for 6–12 hours: IV phytomenadione

2) If surgery cannot be delayed, dried prothrombin complex and IV phytomenadione. INR checked before surgery

Question 21

Combined anticoagulant and antiplatelet therapy can be offered to individuals where indicated after discussion with cardiologist. outline which drugs are used in dual therapy and those used in triple therapy

Answer 21

1) Dual therapy : Aspirin and warfarin sodium
2) Triple: Aspirin with clopidogrel and warfarin
duration of treatment should be kept to a minimum where possible

Question 22

which of the following carries a higher risk of bleeding:

1) Aspirin + Warfarn
2) Clopidogrel + Warfarin

Answer 22

clopidogrel and warfarin carry a higher risk of bleeding

Question 23

In order to keep the length of time as minimal as possible in those on dual or triple therapy, what can be done?

Answer 23

It may be possible to withhold antiplatelet therapy until warfarin therapy is complete, or vice versa