The relationship between adherence and quality of treatment with vitamin K antagonists.

Objective To assess the relationship between adherence and quality of treatment with vitamin K antagonists. Methods Patients diagnosed with atrial fibrillation and treated with acenocoumarol were eligible. The percentage of time spent in the target range during the last three months was calculated using linear interpolation. Adherence was assessed with a self-report questionnaire. Results Forty patients who spent 100% (high-quality group) and 40 patients who spent less than 50% of time in the target range were approached for the study. Twenty-seven patients with high and 29 patients with low therapeutic quality returned the questionnaire. In the high-quality group, 88% of patients reported to have taken all prescribed medication in the previous month, 96% reported to have been fully compliant in the previous week, and 76% reported to have taken all their tablets on time in the previous week. These percentages were 82, 90, and 72, respectively in the low-quality group. Differences between the groups were not statistically significant. Conclusion The results indicate that adherence is not related to time spent in the therapeutic target range in older patients with atrial fibrillation treated with vitamin K antagonists.