The Simplified Medication Adherence Questionnaire: validation of a Brazilian-Portuguese version in hypertensive adults

Background: Self-reported adherence scales are widely used in research and practice because they are low in cost and easy to apply. A free version in Brazilian-Portuguese of the Simplified Medication Adherence Questionnaire (SMAQ) can be a useful alternative for determining the adherent behavior of hypertensive patients. Purpose: To translate and evaluate the psychometric properties of the Brazilian-Portuguese version of the SMAQ therapeutic adherence scale for patients with arterial hypertension. Patients and methods: A multicenter, cross-sectional study was conducted in five outpatient units in Maceió-AL and Aracaju-SE between January and July 2019. A total of 117 patients aged over 18 years using antihypertensive drugs were recruited. The cross-cultural adaptation followed international methodological recommendations. Internal consistency (Cronbach’s alpha) was tested as a reliability parameter. Criterion and construct validity were verified by concurrent validation, exploratory factor analysis (EFA), and validation by known groups. Results: The participants had a mean age of 56.6 years (SD = 10.7 years); most were female (72.6%). The mean number of antihypertensives prescribed per patient was 1.87 (SD = 0.87). There were 79.5% ( n = 86) of patients considered non-adherent. Internal consistency was satisfactory (Cronbach’s alpha = 0.63). A satisfactory correlation coefficient was verified with the Morisky–Green–Levine test as an external criterion ( r = 0.56, p < 0.001). The scale’s sensitivity measured through known group validity was 75.3%, specificity 29.5%, positive predictive value 63.9%, and negative predictive value 41.9%. We identified two factors of the instrument’s construct from EFA: specific medication-taking behaviors and barriers to adherence. The initial KMO measure of sampling adequacy was 0.691, and Bartlett’s test of sphericity was significant (χ 2 = 118.342, p < 0.001). Conclusion: The Brazilian-Portuguese version of the SMAQ scale proved valid and reliable for determining adherence to the pharmacotherapy in hypertensive patients. It showed more ability to detect non-adherent patients but with low specificity, possibly influenced by high social desirability.