Factors Affecting Warfarin Related Knowledge and INR Control of Patients Attending Physicians and Pharmacists’ Managed Anticoagulation Clinics

We have read with a great interest the article entitled “Factors Affecting Warfarin Related Knowledge and INR Control of Patients Attending Physicians and Pharmacists’ Managed Anticoagulation Clinics” by Hasan et al which has been published online in Journal of Pharmacy Practice. ¹

We would like to comment on the article by referring to our study on predisposing preventable factors among patients admitted to the emergency department with bleeding due to warfarin usage. ² Our study was performed on 114 cases who were admitted to emergency service due to complaints of bleeding due to warfarin usage. The sociodemographic characteristics, information on warfarin usage, and their bleeding history are collected by a structured questionnaire form. The mean age of our patients was 66.65 ± 13.57 years (mean ± standard deviation, 27-89 years, 82 cases ≥60 years) and 61 (53.5%) of them were females.

In Hasan et al’s study, patients on warfarin scored an average of 66.5 ± 36% for their knowledge on the mechanism of action of warfarin, 42.9 ± 44.9% for their knowledge on the interaction between warfarin and alcohol, and 49.2 ± 21.1% for their knowledge on the side effects of warfarin. Forty-eight of the patients (42.1%) knew that they had to use this drug under the regular follow-up of a physician and 43 (37.7%) knew that during monitoring a laboratory test had to be done while using the drug named warfarin in our study. Only 39 patients (34.2%) knew this drug may cause bleeding. It was also surprising that only 9 of the patients were aware that there might be an interaction with concomitant drugs and 1 knew that this drug may be affected from the dietary factors.

In Hasan et al’s study, there was a significant difference between patients’ age and knowledge on the mechanism of action of warfarin (P = .001), the interaction between warfarin and alcohol (P = .004), and the side effects of warfarin (P = .013). The correlation analysis showed that there was a negative correlation between age and knowledge on the mechanism of action of warfarin (P = .001), the interaction between warfarin and alcohol (P = .001), and the side effects of warfarin (P = .001). There was no statistically significant difference between the weekly warfarin doses used by the 82 cases who are ≥60 years and the 32 cases who are <60 years (30.1 ± 10.4 mg/week and 33.9 ± 11.9 mg/week, respectively; P = .107) in our study. In our study, although the weekly dose of warfarin was lower, the duration between the onset of warfarin and the time of bleeding is shorter and the bleeding frequency within the first month of treatment is higher among the ≥60 years age group (82 cases) when compared to patients younger than 60 years (32 patients); no statistically significant difference is found. Actually, in the literature, there are such studies in which the relationship between the older age and bleeding risk could not be shown like our study. ^{3 –5}

According to the findings for their study, Hasan et al suggested that patients had satisfactory knowledge regarding the mechanism of action of warfarin and poor knowledge on the interaction between warfarin and alcohol as well as the side effects of warfarin. But, our patients who were admitted to the emergency service with bleeding have a big gap of knowledge which invited bleeding. Most patients were using drugs which are known to interact with warfarin metabolism while using warfarin. Therefore, data given by Hasan et al on the relationship between knowledge regarding the mechanism of action of warfarin and bleeding history of patients should be reevaluated.

As a result, it is important developing a training program for the related specialists and general practitioners who follow-up such patients may have an effect on decreasing the morbidity and mortality caused by warfarin-induced hemorrhages.