Trends in antihypertensive drug utilization in British Columbia, 2004-2019: a descriptive study

Abstract

Background: Clinical guidelines for hypertension were updated with lower blood pressure targets following new studies in 2015; the real-world impact of these changes on antihypertensive drug use is unknown. We aimed to describe trends in antihypertensive drug utilization from 2004 to 2019 in British Columbia.

Methods: We conducted a longitudinal study to describe the annual prevalence and incidence rate of use of 5 antihypertensive drug classes (thiazides, angiotensin-converting enzyme [ACE] inhibitors, angiotensin II receptor blockers [ARBs], calcium channel blockers and β-blockers) among BC residents aged 30-75 years. We also conducted a cohort study to compare the risk of discontinuation and switch or add-on therapy between incident users of the above drug classes. We used linkable administrative health databases from BC. We performed a Fine-Gray competing risk analysis to estimate subhazard ratios.

Results: Among BC residents aged 30-75 years (population: 2 376 282 [2004] to 3 014 273 [2019]), the incidence rate of antihypertensive drug use decreased from 23.7 per 1000 person-years in 2004 to 18.3 per 1000 person-years in 2014, and subsequently increased to 22.6 per 1000 person-years in 2019. The incidence rate of thiazide use decreased from 8.9 per 1000 person-years in 2004 to 3.2 per 1000 person-years in 2019, and incidence rates for the other drug classes increased. Incident users receiving thiazide monotherapy had an increased risk of discontinuing any antihypertensive treatment compared with ACE inhibitor monotherapy (subhazard ratio 0.96, 95% confidence interval [CI] 0.95-0.97), ARB monotherapy (subhazard ratio 0.84, 95% CI 0.81-0.87) and thiazide combination with ACE inhibitor or ARB (subhazard ratio 0.86, 95% CI 0.84-0.88), and had the highest risk of switching or adding on.

Interpretation: First-line use of thiazides continued to decrease despite a marked increase in incident antihypertensive therapy following updated guidelines; incident users receiving ARB monotherapy were least likely to discontinue, and incident users receiving thiazide monotherapy were more likely to switch or add on than users of other initial monotherapy or combination. Further research is needed on the factors influencing treatment decisions to understand the differences in trends and patterns of antihypertensive drug use.

Figure 1:

Prevalence and incidence of antihypertensive drug use among residents of British Columbia aged 30–75 years between 2004 and 2019. Prevalence was computed as the number of prevalent users of thiazides, angiotensin-converting enzyme inhibitors, angiotensin II receptor blockers, calcium channel blockers or β-blockers divided by the number of BC residents aged 30–75 years during the calendar year. Incidence was computed as the number of incident users of the 5 antihypertensive drug classes per 1000 person-years of health plan enrolment among BC residents aged 30–75 years during the calendar year. Prevalent use was defined as at least 1 of the 5 antihypertensive drug classes dispensed during the year. Incident use was defined as 1 of the 5 antihypertensive drug classes dispensed in the absence of a record for any antihypertensive drug dispensed in the 5 years prior (drug list available in Appendix 1, Supplementary Table S2 [www.cmajopen.ca/content/11/4/E662/suppl/DC1]).

Figure 2:

Prevalence of antihypertensive drug use among residents of British Columbia aged 30–75 years between 2004 and 2019, by drug class. Prevalence was computed as the number of prevalent users of an antihypertensive drug class divided by the number of BC residents aged 30–75 years during the calendar year. Note: ACE = angiotensin-converting enzyme, ARB = angiotensin II receptor blocker, CCB = calcium channel blocker.

Figure 3:

Incidence of antihypertensive drug use among residents of British Columbia aged 30–75 years between 2004 and 2019, by drug class. Incidence was computed as the number of incident users per 1000 person-years of health plan enrolment among BC residents aged 30–75 years during the calendar year. Incident use was defined as 1 of the 5 antihypertensive drug classes dispensed in the absence of a record for any antihypertensive drug dispensed in the 5 years prior (drug list available in Appendix 1, Supplementary Table S2 [www.cmajopen.ca/content/11/4/E662/suppl/DC1]). Note: ACE = angiotensin-converting enzyme, ARB = angiotensin II receptor blocker, CCB = calcium channel blocker.

Figure 4:

Cumulative incidence of discontinuation of any antihypertensive therapy by initial drug class. Discontinuation was assigned using the refill-sequence model, in which the first medication-free gap of 90 days for any antihypertensive drug was considered discontinuation of antihypertensive therapy (drug list available in Appendix 1, Supplementary Table S2 [www.cmajopen.ca/content/11/4/E662/suppl/DC1]). The discontinuation date was defined as the expected date of the next prescription refill. The cumulative incidence estimates accounted for death as a competing event. Individuals who were event-free were censored at the end of health plan enrolment or end of follow-up (Dec. 31, 2019). Note: ACE = angiotensin-converting enzyme, ARB = angiotensin II receptor blocker, CCB = calcium channel blocker.

Figure 5:

Cumulative incidence of a switch to or add-on of a different antihypertensive drug class by initial drug class. Switch or add-on therapy was defined as the first dispensing of an antihypertensive drug class different from the initial drug class (drug list available in Appendix 1, Supplementary Table S2 [www.cmajopen.ca/content/11/4/E662/suppl/DC1]). Switching from a combination product to its different components was not considered a switch or add-on event. The cumulative incidence estimates accounted for discontinuation and death as competing events. Individuals who were event-free were censored at the end of health plan enrolment or end of follow-up (Dec. 31, 2019). Note: ACE = angiotensin-converting enzyme, ARB = angiotensin II receptor blocker, CCB = calcium channel blocker.