Case Studies

Case 1

JT is a 55-year-old man with a past medical history of chronic kidney disease, type 2 diabetes mellitus, and hypertension. He is admitted to the hospital for community-acquired pneumonia, and during his stay he is also diagnosed with new-onset nonrheumatic atrial fibrillation (AF). The resident who presents JT on rounds knows that recent changes were made to the American College of Chest Physicians guidelines for stroke prevention in AF, but he does not remember the specifics. He asks the clinical pharmacist whether dabigatran would be appropriate for stroke prevention in this patient.

How should the pharmacist respond?

Case 2

CP is a 61-year-old otherwise healthy man scheduled to undergo a total hip replacement. The surgical team decides to start enoxaparin, a low-molecular-weight heparin, after his surgery for venous thromboembolism (VTE) prophylaxis. During rounds on the surgical floor, the clinical pharmacist reviewed the patient’s medical chart and decides to visit the patient to address any questions. The patient mentions that he is ready for surgery but is concerned about having to be on a blood thinner for a long time after his surgery.

How should the pharmacist respond?

Answers:

Case 1:

According to the 9th edition of the American College of Chest Physicians Antithrombotic Therapy and Prevention of Thrombosis guidelines (or CHEST guidelines), the choice of initial anticoagulation agent in patients diagnosed with AF is based on their risk of stroke as determined by the CHADS₂ score. The CHADS₂ score is calculated based on the presence of patient characteristics including congestive heart failure, hypertension, age greater than 75 years, diabetes mellitus and prior stroke or transient ischemic attack (TIA). One point is given for each characteristics present, with two points given for prior stroke/TIA. In patients with a low risk of stroke (CHADS₂ score=0), no prophylaxis is needed (although if treatment is initiated, aspirin 75-325 mg once daily is recommended over other therapies). In patients with an intermediate or high stroke risk (CHADS₂ score of 1 or higher), guidelines recommend oral anticoagulation over no therapy, aspirin, or the combination of aspirin and clopidogrel. The guidelines also recommend dabigatran 150 mg twice daily over adjusted-dose warfarin; however, because dabigatran is primarily excreted via the kidneys, it is contraindicated in patients with a creatinine clearance less than 30 mL/min.

JT has a high risk of stroke based on his CHADS₂ score of 2 (one point each for diabetes and hypertension). While dabigatran 150 mg twice daily may be a reasonable choice, because JT has a history of CKD, it would be important to determine his estimated creatinine clearance before making a decision. If it is lower than 30 mL/min, anticoagulation with warfarin with a target INR of 2 to 3 should be selected instead.

Case 2:

The 9th edition of the American College of Chest Physicians Antithrombotic Therapy and Prevention of Thrombosis guidelines (or CHEST guidelines) recommend LMWH as the preferred agent in patients undergoing major orthopedic surgery. Alternative medications include fondaparinux, low-dose unfractionated heparin, adjusted-dose warfarin, or aspirin. Apixaban, dabigatran and rivaroxaban are also alternatives suggested in patients undergoing total hip or knee replacement, but only rivaroxaban is approved for this indication and available in the US. Currently, the guidelines suggest VTE prophylaxis be continued for up to 35 days after major orthopedic surgery as it further reduces the incidence of post-surgical VTE without an appreciable increase in major bleeding risk .

The pharmacist should inform CP that he will start his anticoagulation with enoxaparin 12 hours after his surgery and continue it for a total of 35 days. Since CP’s risk for a clot is highest during this time period, the importance of good medication adherence should be reinforced.

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Dr. Coleman is associate professor of pharmacy practice and director of the pharmacoeconomics and outcomes studies group at the University of Connecticut School of Pharmacy. Drs. Sobieraj and Dabek are pharmacists affiliated with the University of Connecticut School of Pharmacy