Persistence to antihypertensive drug treatment in Swedish primary care

Abstract

The efficacy of antihypertensive drug therapy is undisputed, but large surveys report that one in four patients reach a target blood pressure of <140/90 mm Hg. Although there are several explanations to this problem, poor medication adherence and persistence to drug treatment suggests as important contributors.

We started with a cross-sectional study design, to describe drug prescription patterns and blood pressure control in 24 primary healthcare centers in southwestern part of Stockholm, Sweden. Electronic medical records of 21167 patients (≥30 years) with a diagnosis of hypertension and a consultation at one of the included primary health care centers in 2005-2006 were analyzed. A prescription of an antihypertensive drug were found in 89% of the patients, and the most common were the diuretics and beta blockers. One out of four primary care patients with hypertension had a target blood pressure <140/90 mm Hg with or without antihypertensive drug treatment.

Medication persistence is considered an important factor to poor blood pressure control. Therefore, in the subsequent project, we used a cohort study design to measure persistence after two years of follow-up and analyzed factors associated with low therapy persistence, i.e. persistence to any antihypertensive drug class treatment. Using electronic medical records for patients with hypertension in 48 Swedish primary healthcare centers and data linkage to national registers on dispensed drugs, hospitalizations, outpatient hospital consultations, deaths, migration, and socioeconomy, we were able to identify 5225 patients initiated on antihypertensive drug treatment during 2006-2007. Among patients with a dispensed first prescription, 65 % were persistent after the two years of follow-up. Factors associated with low therapy persistence to antihypertensive drug treatment were male sex, younger age, mild-to-moderate systolic blood pressure elevation, and birth outside of Sweden.

After the assessment of therapy persistence, an important question remained, and that was to answer if there was a difference in persistence to the various antihypertensive drug classes? Again, we performed a cohort study with the same method described above, but analyzed each antihypertensive drug class in comparison to the diuretics. It appeared to be no difference in drug class persistence between diuretics and the other major antihypertensive drug classes. Predictors behind low class persistence were the same as for therapy persistence.

Although register studies are of interest and of great value, they lack certain information. To get a broader picture of the medication persistence, we decided to perform a cross-sectional study and use questionnaires to ask the patients about their beliefs about medicines and the hypertension diagnosis. The questionnaires were linked with data on the patient’s filled prescription and the patients were categorized into persistent or non-persistent medication-users, to observe potential differences in the attitudes between the persistent and non-persistent patients. Out of the 69 primary healthcare centers questioned, 25 agreed to participate in the study. In January 2016, patients with a diagnosis of hypertension and a consultation at one of the 25 primary health care centers received a questionnaire 3-12 months after initiation of drug treatment. Out of the 1197 patients newly initiated antihypertensive drug treatment, 711 patients (59%) responded. Patients were classified as persistent (609, 86%) or non-persistent (102, 14%) to antihypertensive drug treatment by analyses of their filled prescriptions. Compared to non-persistent medication users, patients persistent to medication believed to a higher degree that the diagnosis of hypertension was chronic, that it had less consequence on their life, that they can prevent cardiovascular disease by taking antihypertensive drug treatment and that there is something positive about taking the pharmacological treatment.