A 54-year-old man comes to the emergency department with pain and swelling in the right leg. The patient has no other medical problems and takes no medications. He has smoked a pack of cigarettes daily for the past 30 years. He is a business executive and just returned from an overseas trip. Physical examination shows pitting edema of the right leg and tenderness on deep palpation of the calf muscles. Peripheral pulses are symmetric and full. He is started on a medication that prolongs activated partial thromboplastin time and prothrombin time in a dose-dependent manner but has no effect on thrombin time. Which of the following agents was this patient most likely administered?

Question

A 54-year-old man comes to the emergency department with pain and swelling in the right leg.  The patient has no other medical problems and takes no medications.  He has smoked a pack of cigarettes daily for the past 30 years.  He is a business executive and just returned from an overseas trip.  Physical examination shows pitting edema of the right leg and tenderness on deep palpation of the calf muscles.  Peripheral pulses are symmetric and full.  He is started on a medication that prolongs activated partial thromboplastin time and prothrombin time in a dose-dependent manner but has no effect on thrombin time.  Which of the following agents was this patient most likely administered?

Quizplus · Accepted Answer

11ec160b_3aee_74d7_9249_79e25a0ef3e4_MD0001_00 This patient has deep venous thrombosis, which is typically treated with anticoagulation therapy for >3 months to prevent recurrent thrombosis. Initial treatment is often with heparin agents (eg, unfractionated heparin, low-molecular-weight heparin, fondaparinux), followed by bridging to an oral anticoagulant (most commonly warfarin). Additional treatment options include direct factor Xa inhibitors (eg, apixaban, rivaroxaban) and direct thrombin inhibitors (eg, dabigatran). In general, medications that affect the extrinsic pathway prolong the prothrombin time (PT), whereas inhibition of the intrinsic pathway mainly prolongs the activated partial thromboplastin time (aPTT). The thrombin time (TT) is prolonged with medications that directly or indirectly inhibit thrombin. Because factor Xa is located at the junction of the intrinsic and extrinsic pathways, direct factor Xa inhibitors prolong both aPTT and PT with no effect on TT. (Choice A) Cyclooxygenase inhibitors (eg, aspirin) directly inhibit platelet activity and have little overall effect on aPTT, PT, or TT. (Choice B) Direct factor VIIa inhibitors are currently in development and work by inhibiting the extrinsic pathway of the coagulation cascade. Therefore, they would prolong PT with no effect on aPTT or TT. (Choice D) Direct thrombin inhibitors (eg, dabigatran) prevent the formation of thrombin (factor IIa), resulting in prolongation of aPTT, PT, and TT. (Choice E) Unfractionated heparin binds to antithrombin and causes inactivation of several coagulation factors, most significantly thrombin and factor Xa. As a result, aPTT and TT will be prolonged. Although the PT should theoretically be prolonged by the action of heparin on the final common pathway, in practice, the PT reagent contains heparin neutralizers that minimize this effect. Educational objective: Direct factor Xa inhibitors (eg, apixaban, rivaroxaban) increase the prothrombin and activated partial thromboplastin times but do not affect the thrombin time. Unfractionated heparin and direct thrombin inhibitors (eg, dabigatran) prolong the thrombin time. __________ References: Developments in factor Xa inhibitors for the treatment of thromboembolic disorders (http://www.ncbi.nlm.nih.gov/pubmed/19967784)

A 54-Year-Old Man Comes to the Emergency Department with Pain