Poor adherence to warfarin therapy significantly affects anticoagulation control

Patients who fail to adhere to warfarin therapy as prescribed are more likely to experience problems with anticoagulation control, according to the authors of the International Normalized Ratio Adherence and Genetics (IN-RANGE) study.

Key Points

Patients who fail to adhere to warfarin therapy as prescribed are more likely to experience problems with anticoagulation control, according to the authors of the International Normalized Ratio Adherence and Genetics (IN-RANGE) study published in the journal Archives of Internal Medicine.

"Adherence to long-term medication regimens, including cardiovascular therapies, is a major challenge facing patients and healthcare providers," the authors stated. "This is particularly true for narrow therapeutic index drugs such as warfarin."

In this prospective cohort study involving 3 anticoagulation clinics in Pennsylvania, 136 patients were treated with warfarin for various indications (with a goal international normalized ratio [INR] of 2–3). Adherence to anticoagulation therapy was monitored using electronic Medication Event Monitoring System (MEMS) medication bottle caps. After using multivariate logistic regression to adjust for factors that might affect a patient's response to warfarin, it was demonstrated that every 10% increase in missed pill-bottle-openings was associated with a 14% increase in the odds of under-anticoagulation (defined as INR <2; P<.001). The odds of under-anticoagulation were increased 100% for patients who missed >20% bottle openings (adjusted OR=2.10; 95% CI, 1.48–2.96).

"This study demonstrates that poor adherence is potentially a major source of poor anticoagulation control, even among patients being treated in specialized anticoagulation clinics where the importance of adherence is constantly emphasized," the authors stated.

It is estimated that poor patient adherence to medications is responsible for more than 5.3% of all hospital admissions at a cost of more than $8 billion.

SOURCE Kimmel SE, Chen Z, Price M, et al. The influence of patient adherence on anticoagulation control with warfarin: Results from the International Normalized Ratio Adherence and Genetics (IN-RANGE) study. Arch Intern Med. 2007;167:229–235.