Warfarin underused in the most at-risk population

By: Alere Staff
Publication Date: Tue, 11/01/2011

The number of patients that use warfarin continues to increase as the population ages. Despite this growth in warfarin use, a national survey conducted in Ireland revealed that only 26% of patients with atrial fibrillation over 75 years old receive warfarin. Geriatrician expert and investigator, Laurie Jacobs, MD, notes that the elderly are at greatest risk for stroke but are often under-treated.1

Dr. Jacobs explains that, “elderly patients as a group may present more of a challenge in managing warfarin therapy because of alterations in pharmacokinetics from other medications, diet, and disease; pharmacodynamic changes; increased risk for hemorrhage; and difficulty monitoring. The elderly, however, may derive the most benefit from warfarin therapy.”1

Management challenges

The under-use of warfarin can sometimes be attributed to the physician perception that the risk of bleeding is too high. Management of the medication’s narrow therapeutic index is further complicated by concomitant medication use and dietary interactions.1

Patient education and consistent vitamin K consumption are recommended. Dr. Jacobs suggests that patients examine nutritional labeling and discuss dietary supplements with a healthcare provider. Chronic alcohol use increases the clearance of warfarin, whereas liver disease can potentiate the effect of warfarin. In contrast to information found in the package insert for warfarin, a 1998 study published in the American Journal of Health System Pharmacists showed that grapefruit juice had little impact on the anticoagulation effect of warfarin.1

Initiating therapy

Elderly patients at immediate risk for thromboembolism are often given heparin or low molecular weight heparin, which is continued until a therapeutic International Normalized Ratio (INR) is achieved. Jacobs cited several studies that demonstrate no benefit to load dosing when initiating warfarin therapy in the elderly population. It is no longer recommended in the warfarin package insert. One study found that 5mg of warfarin was superior to 10mg for dosing initiation, while another study showed that initiating elderly patients at 2.5 mg of warfarin was superior to 5mg.1

Monitoring elderly patients

Dr. Jacobs notes that, “the optimal frequency of INR testing to maintain patients within therapeutic range is not clear.”1 Medicare, however, announced expanded reimbursement coverage to support weekly home testing for elderly warfarin patients that are eligible for Medicare benefits.2 Increased testing frequency was found to reduce the risk of warfarin side effects, including increased risk of bleeding, which prompted the expanded coverage initiated by the Center for Medicare and Medicaid Services (CMS).

Systematic care prevails

Systematic care includes coordinated patient care processes. Point-of-care monitors provide physicians the flexibility to obtain INR test results in patient homes, doctor offices, and clinics. Studies have shown that standard care, which involves venous sampling and external laboratories, results in lower time in target range (34%-64%) when compared to systematic care using portable INR monitors (61% to 92%).Time in target range for patients who use point-of-care testing at home ranges between 56% to 93%.1

  1. Jacobs, L. (2008). Warfarin Pharmacology, Clinical management, and evaluation of hemorrhagic risk for the elderly. Cardiology Clinic, 157-167.
  2. Center for Medicare and Medicaid Services. (2008). Decision Memo for Prothrombin Time (INR) Monitor for Home Anticoagulation Management  (CAG-00087R) [Memorandum]. Baltimore, MD.