Background: Although a majority of patients with hypertension require a multidrug therapy, this is rarely considered when measuring adherence from refill data. Moreover, investigating the association between refill non-adherence to antihypertensive therapy (AHT) and elevated blood pressure (BP) has been advocated.
Objective: Identify factors associated with non-adherence to AHT, considering the multidrug therapy, and investigate the association between non-adherence to AHT and elevated BP.
Methods: A retrospective cohort study including patients with hypertension, identified from a random sample of 5025 Swedish adults. Two measures of adherence were estimated by the proportion of days covered method (PDC≥80%): (1) Adherence to any antihypertensive medication and, (2) adherence to the full AHT regimen. Multiple logistic regressions were performed to investigate the association between sociodemographic factors (age, sex, education, income), clinical factors (user profile, number of antihypertensive medications, healthcare use, cardiovascular comorbidities) and non-adherence. Moreover, the association between non-adherence (long-term and a month prior to BP measurement) and elevated BP was investigated.
Results: Non-adherence to any antihypertensive medication was higher among persons < 65 years (Odds Ratio, OR 2.75 [95% CI, 1.18-6.43]) and with the lowest income (OR 2.05 [95% CI, 1.01-4.16]). Non-adherence to the full AHT regimen was higher among new users (OR 2.04 [95% CI, 1.32-3.15]), persons using specialized healthcare (OR 1.63, [95% CI, 1.14-2.32]), and having multiple antihypertensive medications (OR 1.85 [95% CI, 1.25-2.75] and OR 5.22 [95% CI, 3.48-7.83], for 2 and ≥3 antihypertensive medications, respectively). Non-adherence to any antihypertensive medication a month prior to healthcare visit was associated with elevated BP.
Conclusion: Sociodemographic factors were associated with non-adherence to any antihypertensive medication while clinical factors with non-adherence to the full AHT regimen. These differing findings support considering the use of multiple antihypertensive medications when measuring refill adherence. Monitoring patients' refill adherence prior to healthcare visit may facilitate interpreting elevated BP.