Determinants of discontinuation of new courses of antihypertensive medications

Abstract

Discontinuation of medication use constitutes a major barrier to adequate control of high blood pressure. We examined the effect of an array of potential predisposing, enabling and reinforcing factors on the discontinuation of newly prescribed antihypertensive medications. We conducted a prospective cohort study through a network of 173 pharmacies across Canada where were identified individuals newly prescribed an antihypertensive monotherapy. We interviewed participants by telephone four times to obtain information for a minimum duration of 18 months after entry into the cohort. We analyzed data using a multivariate proportional hazard model. Of 682 eligible participants, 43.3% had discontinued their initial medication at the end of the observation period. Individuals more likely to discontinue their initial medication were those who perceived side effects from this medication [Hazard Ratio (HR) = 1.91; 95% Confidence Interval (CI) 1.47–2.47). Individuals with medication insurance coverage were less likely to discontinue (HR = 0.74; 95% CI 0.55–0.99). Persistence with newly prescribed medications could be improved by selecting antihypertensive medications containing fewer side effects and by lifting economic barriers to drug treatment.

Introduction

Cardiovascular disease is still the leading cause of mortality in the developed world. Despite evidence that blood pressure control may reduce premature cardiovascular mortality 1, 2, and despite the availability of effective treatment for high blood pressure, a high proportion of identified hypertensive individuals are not controlled (mean diastolic or systolic blood pressure greater than 90 mmHg or 140 mgHg, respectively) 3, 4, 5.

Poor adherence including discontinuation of the recommended drug regimen constitutes a major barrier to adequate control of high blood pressure [3]. Indeed, providing there has not been a life style behavioral modification to compensate, individuals with established hypertension can no longer benefit from a reduction in their blood pressure if they stop the use of antihypertensive drugs. For those who are persisting with drug therapy, poor adherence is likely to interfere with a satisfactory treatment outcome.

Previous studies have focused on discontinuation of newly prescribed antihypertensive drugs 6, 7, 8, 9. Estimates of the proportion of those patients still on initial treatment after a few months, have varied from study to study, but generally it is poor: less than 50% of patients continue their initial treatment after 12 months 6, 7. Among those who persist on antihypertensive therapy, around 20% experience a modification in their initial treatment [8].

Some studies, mostly analyses of administrative databases, have so far shown that discontinuation of antihypertensive drug treatment is associated with younger patients as opposed to older ones 7, 9, with men as opposed to women [9], and to a regimen dosing of more than once a day [7]. These studies did not explore patient characteristics such as their perception of health, beliefs about the disease, and about the efficacy of its treatment, as potential determinants of discontinuation of treatment.

This study was designed to examine the effect of an array of potential predisposing, enabling and reinforcing factors on the discontinuation of initial antihypertensive medication. We conducted a prospective cohort study in a community-based setting of individuals newly prescribed antihypertensive monotherapies.