IJCS | Volume 31, Nº4, July / August 2018

384 Borges et al. Adherence score Int J Cardiovasc Sci. 2018;31(4)383-392 Original Article adherence. Studies have so far highlighted the importance of health education as an efficient strategic intervention to improve the use of oral anticoagulants (OACs) but have not provided enough evidence on instruments to measure adherence and non-adherence. Finally, the study support the emerging need for a medication adherence scale for this population. 4 In light of this context and current recommendations, a need for the development of a score to assess adherence and non-adherence in users of OACs has emerged. Methods This was an analytical, observational, cross-sectional study, with a quantitative approach, conducted at theOral Anticoagulation Center of a public, cardiology hospital associated to the São Paulo State Secretary of Health. For sample calculation, we considered the prevalence of altered INR (international normalized ratio), i.e., 5% among patients without other conditions that may affect this parameter; 15% among patients with conditions that may affect this parameter, additionally to an alpha of 5% and power of 95%. Therefore, inclusion of 5 and 2 patients with and without factors known to affect INR, respectively, was considered, resulting in a sample size of 574. An additional 5% was considered for possible dropouts, yielding a sample of 607 patients on OAC-T that met eligibility criteria. Altered INR was used as outcome measure and the following predicting variables were assessed: drug handling, drug-drug and drug-food interactions, surgeries and other procedures, clinical condition, health problems, among other factors – stress, weight loss / gain, use of (generic or similar) warfarin, alcohol abuse and physical activity. Data collection was performed in two stages – in phase I, general features of the sample were collected, and in phase II, clinical characteristics were collected. All patients signed an informed consent form before being included in the study. The study was approved by local ethics committee (approval number 4420; CAAE: 24118513.7.0000.5392). Statistical analysis Qualitative variables were expressed as absolute and relative frequency, and quantitative variables as mean and standard deviation. The chi-square test and Fisher’s exact test were used to assess associations between qualitative variables. Variables with p < 0.10 and/or with clinical significance for adherence and INR within recommended therapeutic range were analyzed by a multiple logistic regression model, followed by a stepwise backward analysis for the final model. C-statistic was calculated by the ROC (receiver operating characteristic) curve to evaluate the final model and final score. Significance level was set at 5%. Analysis was performed using the Statistical Package for Social Sciences (SPSS) version 19 (Armonk, NY: IBM Corp.) and the R Core Team 2016 software. Results Clinical profile of users of OACs A total of 607 patients on OAC-T participated in the study. Fifty-two percent of patients were women, 57% married, 56% older than 60 years, 42% had some elementary school, in 55% the family incomewas between 1 and 3 minimum wage, and almost all of them (93%) came from Sao Paulo. Sociodemographic characteristics are described in Table 1. Normal INR levels used as reference were: < 2 and > 3 for patients with thromboembolic events, and < 2.5 and > 3.5 for patients with mechanical prosthesis. Forty percent of patients (n = 247) had altered INR, whereas 60% (n = 360) had normal INR. Most INR results were within the range from 2 to 3, whereas 119 participants (36%) with mechanical prosthesis had an INR < 2.5 and > 3.5. In addition, the presence of atrial fibrillation and/or atrial flutter was considered for patients withmechanical prosthesis. Most Table 1 - Sociodemographic characteristics of patients on oral anticoagulation therapy (n = 607) Variables Nº % Female sex 315 52 Age > 60 years 341 56 Married 348 57 Some elementary school 280 42 Family income (1 - 3 minimum wages) 332 55 Patients with MP and altered INR 119 36 Evidence of thromboembolism with altered INR 105 54 MP: mechanical prosthesis; INR: international normalized ratio.