Objectives: Most patients with hypertension need combination therapy to reach adequate blood pressure control. The objective of this study was to assess type, duration of, and adherence to antihypertensive therapies among veterans, focusing on the use of combination therapies.
Research design and methods: The design of the study was a retrospective cohort analysis of electronic medical and pharmacy records from the Central Texas Veterans Health Care System (CTVHCS). Data were extracted for adults newly identified with hypertension between 1995 and 2003. Drug utilization was measured as a time-dependent variable; thus, the use of combination therapies was captured for any given day for each patient in the sample. Medication adherence was assessed using medication possession ratios (MPR), calculated by the number of days of therapy dispensed to a patient divided by the number of days between subsequent prescriptions.
Results: The average age of the participants (n = 11 187) was 60.7 (standard deviation (SD): 12.7). Half (50.1%) of the patients could be categorized as having controlled blood pressure. Veterans were followed for an average of 3.6 years (total of 51 549 person-years). Overall, 29 561 treatment episodes were identified, an average of about 2.6 per patient. Over 40% (41.6%) of these episodes involved one medication only, but patients frequently used dual (26.9%) and three or more (15.9%) therapies in combination. The frequency of prescribed antihypertensive therapies, as well as the length of, and adherence to, these therapies were described. Descriptively, medication adherence appeared to be lower among patients who received therapy for longer duration, indicating higher probability of missed doses and more frequent therapy changes.
Conclusions: New information can be gained on the utilization of antihypertensive medications by using time-dependent variables. Understanding the type of combination therapies, the length of and adherence to these therapies, along with the observed blood pressure control rates will provide important new insights into the management of hypertensive patients. Limitations of the study arise primarily from the use of electronic medical records and the information that is contained within the datasource, and generalizability of the findings beyond the study sample.