Warfarin control and knowledge suboptimal in HK patients

Time in therapeutic range (TTR) and knowledge about warfarin therapy are suboptimal among local patients receiving the anticoagulant for various indications, an observational study at the Prince of Wales Hospital (PWH) has shown.

In the study, researchers from the Chinese University of Hong Kong (CUHK) examined electronic records of 259 patients (mean age, 67.9 years; male, 48.6 percent) who received warfarin in the acute coronary syndrome registry and warfarin clinic of PWH for at least 1 year from January 2010 to August 2015. The patients’ mean TTR was 40.2 +/- 17.1 percent based on the European therapeutic range, and 49.1 +/- 16.1 percent based on the Japanese therapeutic range (p<0.001). [Hong Kong Med J 2020, doi: 10.12809/hkmj208416]

Only 7.7 percent and 12.4 percent of patients had ideal TTR based on the European and Japanese therapeutic ranges, respectively.

Mean TTR was significantly higher in patients with atrial fibrillation (AF) than in those with prosthetic heart valve (PHV) (48 percent vs 30.5 percent by European therapeutic range; 53.4 percent vs 48 percent by Japanese therapeutic range; p<0.001).

“Younger age, as well as concurrent use of furosemide, famotidine or simvastatin, were predictors of suboptimal TTR,” the researchers reported.

“Warfarin is the most commonly prescribed anticoagulant in Hong Kong. However, warfarin use in Hong Kong patients was poorly controlled, regardless of indication. This poor control was associated with worse clinical and economic outcomes,” the researchers pointed out.

In the study, 35.9 percent of patients experienced complications, including thrombotic events (15.1 percent) and bleeding complications (24.7 percent). Patients with nonideal TTR were more likely to experience overall and bleeding complications than those with ideal TTR.

“All patients who experienced complications were those with nonideal TTR based on the European therapeutic range,” the researchers noted.

In terms of economic outcomes, healthcare costs (including international normalized ratio [INR] examination costs, clinical visit costs, and total healthcare costs) were significantly lower for patients with ideal TTR based on both European and Japanese therapeutic ranges. Hospitalization costs were also lower for patients with ideal TTR based on the Japanese therapeutic range.

The study also revealed poor knowledge about warfarin therapy, as measured by the Oral Anticoagulant Knowledge (OAK) test administered via phone interviews with the patients. The mean OAK score was 54.1 percent among 174 patients who completed the test.

“Only 13.8 percent of patients achieved a satisfactory overall score of at least 75 percent on the OAK test,” the researchers reported. “Patients who were older [p=0.001] or had comorbid diabetes [p=0.03] were more likely to have low scores on the OAK test, while those with comorbid hypertension [p=0.004] or thyroid dysfunction [p=0.003] were more likely to have high scores.”

“Despite the establishment of a warfarin clinic and availability of educational materials and discussions regarding warfarin use, patient knowledge about warfarin therapy remains unsatisfactory,” they commented.

“Patients had poor knowledge about INR value and interpretation. More education is needed about drug-drug interactions of warfarin and the consequences of missed doses,” they continued. “New approaches may be useful for delivery of medication knowledge.”