Anticoagulant Quiz Flashcards
Patients with chronic atrial fibrillation routinely receive warfarin to prevent formation of blood clots in the poorly contracting atrium and to decrease the risk of embolism of such clots to the brain or other tissues. Such patients are also often treated with antiarrhythmic drugs. The primary goals of antiarrhythmic treatment are to slow the atrial rate and, most importantly, control the ventricular rate.
A. Which antiarrhythmic drugs are most appropriate for treating chronic atrial fibrillation?
B. Do any of these drugs have significant interactions with warfarin?
C. Can you name two alternative oral anticoagulants for patients with chronic atrial fibrillation?
A) Group 2 and 4 antiarrhythmics – beta blockers (metoprolol, propranolol) and calcium channel blockers (verapamil, diltiazem) – both slow AV node conduction and ventricular contraction rate.
Other options to treat chronic a fib include group 1 and 3 antiarrhythmics – amiodarone, procainamide, sotalol – can be considered.
B) Amiodarone has a metabolite that interacts with warfarin and prolongs its anticoagulant effect, increasing bleeding risk. None of the other listed options interact with warfarin.
C) Factor Xa inhibitors – rivaroxaban
Direct thrombin inhibitors – dabigatran
Your patient is responding well to warfarin and is stabilized for a month with a consistent INR of 2.2. Drug B is added but everything else stays the same. After starting on Drug B the INR falls and after two weeks stabilizes to 1.6. Drug B is stopped and Drug C is started. the INR increases but after 4 weeks stabilizes at 2.8.
One of the following explanations listed below correctly explains this observation. Which statement is correct?
A) Drug B displaces warfarin from plasma binding proteins, ie enhances warfarin. Drug C is an antagonist to warfarin.
B) Drug B inhibits metabolism of warfarin. Drug C Enhances the activity of drug B.
C) Drug B stimulates metabolism of warfarin. Drug C displaces warfarin from plasma binding proteins. (Drug C Enhances warfarin)
D) Drug B increases renal clearance of warfarin. Drug C inhibits metabolism of Drug B
C – a drug that stimulates the metabolism of warfarin diminishes the warfarin effect (decreases anticoagulant effect, shortens coagulation time). A drug that displaces warfarin from plasma binding proteins enhances the effect of warfarin (increases anticoagulant effect, prolongs coagulation time)
Today’s patient is a 69 year old woman presenting with pain in her left thigh muscle. Duplex ultrasonography indicates the presence of deep vein thrombosis in the affected muscle.
You decide to initiate treatment with enoxaparin. Compared to unfractionated heparin, enoxaparin:
A) Can be used without monitoring the aPTT
B) Has a shorter half life/duration of action
C) Is less likely to have a teratogenic effect
D) Is more likely to be administered IV
E) Is more likely to cause thrombocytopenia
A – enoxaparin is a LMWH. LMWHs have longer half lives than plain or unfractionated heparin, and have a more consistent relationship between dose and effect.
Enoxaparin is most often given SQ rather than IV, and is LESS likely to cause thrombocytopenia. UFH and LMWH do not cross the placenta and are NOT considered teratogens. UFH is usually used in patients who requiring monitoring of the aPTT, or prior to surgery or delivery to take advantage of its shorter duration of action.
Your patient today is a 57 year old woman with chronic hypertension, and type 2 diabetes recently discharged from the hospital for new onset atrial fibrillation and congestive heart failure. You have her hospital record, her echocardiogram and ECG. Her ECG is consistent with atrial fibrillation. According to her risk score she requires anticoagulation rather than anti-platelet therapy. You would like to use a direct thrombin inhibitor. Which of the following is a DTI?
A) Abciximab
B) Dabigatran
C) Rivaroxaban
D) Warfarin
B – abciximab is an antiplatelet agent that binds to GP IIb/IIa, rivaroxaban is an oral factor X inhibitor
Is there a blood test we can order to monitor factor X?
A) aPTT
B) A factor X test
C) INR
D) Anti Factor Xa test
D – the INR reflects the effects of vitamin K antagonists like warfarin. Factor X activity is not reliably measured by the PTT or PT.
