IJCS | Volume 31, Nº4, July / August 2018

385 Borges et al. Adherence score Int J Cardiovasc Sci. 2018;31(4)383-392 Original Article patients on OAC-T with INR < 2.0 were those with atrial fibrillation (n = 105, 54%) (Table 1). For patients with INR > 2 (conditions with risk for thromboembolic events) and/or > 2.5 (mechanical prosthesis), atrial fibrillation was the most frequent disease andmechanical prosthesis was the main valvular prosthesis – mitral valve (n = 58; 26%) and aortic valve (n = 41; 18%). With respect to participants’ diseases and indication for OAC, 30 types of heart diseases were identified, 51% (783) clinical conditions and 24% (360) of surgical type, as well as related comorbidities (364; 25%). Multiple logistic regression model The following variables were selected for the multiple logistic regression model: family income, educational attainment, inadequate doses, invasive procedures, drug interactions, eating habits, physical activity, health problems, OAC-related complications, among other factors (Table 2). Since all predictive variables showed a significative response, seven logistic regression models were considered for analysis at first. However, the model adopted in the study included the variables described in Table 2, considering also the interactions between them. Simonetti medication adherence score The variables used in the scores are shown in Table 3. First, the percentage of adherence was determined by Simonneti SH by multiplying the number of positive variables for adherence by the total number of predictive variables. A score was also developed to determine whether INR was within the normal range (Figure 1). The score was calculated by odds ratio. Then, each condition known to affect INR was categorized into high (≤ 10 points), intermediate (11 – 30 points) and high (≥ 31 points) for normal INR (Figure 2). The area under theROCcurvewas determinedbasedon the results of the variables proposed in the present study (Figure 3). For the logistic model, C-statistic was 0.940 (95%CI = 0.920 – 0.960; p < 0.001), indicating a satisfactory performance in detecting the occurrence of an event. Discussion The optimal dose of OAC is variable between individuals and should be adjusted to ensure that INR is maintained within the therapeutic range. In addition, it is known that the patient may reduce, discontinue (e.g. bleeding) or increase (e.g. double dose to make up for a missed dose) the dose of OAC. 5 OAC-T-related complications may also be associated with the use of Marevan ® , due to underdosing (risk of thrombus formation) or overdosing (bleeding), and the seek for medical care due to gum bleeding, hematuria, and other complications. 6 Therefore, the lack of appropriate instructions and recommendations for patients on OAC-T in the perioperative period of any clinical or surgical procedure may cause variability in routine practice and affect the maintenance of INR within therapeutic range. Nevertheless, evidence shows that changes in OAC-T are not required prior to tooth extraction for example, providing that INR is maintained between 2 and 4, and bleeding control measures are implemented in the perioperative period to prevent embolic events. 7 Studies have suggested that patients on OAC-T may require parenteral anticoagulation in the perioperative period. The decision to discontinue anticoagulation and start an antithrombotic therapy is determined by the risk of bleeding, surgical treatment to which patients were submitted and the risk for thrombosis due to underlying diseases. 8 However, for patients at low risk of bleeding (skin biopsies, cataract or dental procedures), the use of OAC may be continued, providing that INR is maintained at lower values and control of local bleeding is successfully achieved. 8 Due to the risk of bleeding, when management of patients on OAC-T includes major surgery, it is recommended 8 that these individuals are classified into patients at minimal risk (atrial fibrillationwithout history of venous thromboembolism), intermediate risk or high risk of thromboembolism. In addition, one of the main factors that affect INR and treatment adherence is drug-drug interactions. Antonio et al. 7 described the main drugs that interact with and potentiate the effect of OACs – allopurinol, amiodarone, cimetidine, cisapride, clofibrate and other fibrates, chloramphenicol, cotrimoxazole, erythromycin, fluconazole, isoniazid, metronidazole, miconazole, omeprazole, phenylbutazone, piroxicam, propafenone, propranolol, salicylate, phenylbutazone. These drugsmay increase INR and cause bleeding. However, some drugs may inhibit the effects of OAC, including barbiturates, carbamazepine, chlordiazepoxide, cholestyramine,