Blood Pressure Association with the 8-Item Morisky Medication Adherence Scale in Hypertensive Adults from Low-Resource Primary Care Settings: Results from a Prospective Cohort Nested within a Randomised Controlled Trial.

Introduction: One of the self-report adherence scales most widely used is the 8-item Morisky Medication Adherence Scale (MMAS-8).

Aim: To evaluate construct validity and reliability of the MMAS-8 in hypertensive adults from low-resource settings within the public primary care level in Argentina.

Methods: Prospective data from hypertensive adults under antihypertensive pharmacological treatment that participated in the "Hypertension Control Program in Argentina" study was analyzed. Participants were followed at baseline, 6, 12 and 18 months. Based on MMAS-8, adherence was defined as low (score < 6), medium (score 6 to < 8) and high (score of 8).

Results: 1214 participants were included in the analysis. In comparison to low adherence, high adherence category was associated with a reduction of - 5.6 mmHg (CI 95%: - 7.2; - 4.0) in systolic blood pressure (BP) and - 3.2 mmHg (CI 95%: - 4.2; - 2.2) in diastolic BP; and with a 56% higher likelihood to have controlled BP (p < .0001). Among those participants with baseline score ≤ 6, two points increase in MMAS-8 along follow-up showed a tendency to reduce BP in almost all-time points and a 34% higher likelihood of having controlled BP at the end of the follow-up (p = 0.0039). Cronbach's alpha total-item values in all time-points were higher than 0.70.

Conclusions: Higher MMAS-8 categories were positively associated with BP reduction and higher likelihood of BP control over time. Internal consistency was acceptable and in line with previous studies.