Influences of educational interventions and adverse news about calcium-channel blockers on first-line prescribing of antihypertensive drugs to elderly people in British Columbia

Summary

Background

The way in which dissemination of evidence changes medical practice needs to be better understood. Controversy about calcium-channel blockers (CCB) in the past 3 years has provided a natural experiment, enabling assessment of the impact of media stories, a national warning letter, a teleconference, small group workshops, and newsletters on first-line prescribing of antihypertensive drugs.

Methods

We included all physicians (4403) in British Columbia who prescribed a thiazide diuretic, β-blocker, inhibitor of angiotensin-converting enzyme (ACE), or CCB as the first antihypertensive agent for 36 507 residents aged 66 years and over, with no previous or concurrent sign of underlying cardiovascular disease. We used a database covering all prescriptions to elderly people to measure the change in proportion of newly treated patients who received each class of drug as first-line therapy. We used a matched cohort design for assessment of the teleconference and workshops, a randomised community design for the newsletters, and time-series analysis for the media impacts.

Findings

The proportion of patients who received a CCB as first-line therapy declined gradually from 22% in early 1994 to 15% in late 1996. This proportion was not affected by two waves of adverse news about CCBs in 1995, but fell by 5% for 5 months and by 3% for 1 month after two waves in 1996. The proportion of patients who received either a CCB or an ACE inhibitor as first-line therapy, contrary to guidelines, was still 42% overall in 1996. The workshops and newsletters were followed by shifts from first-line CCB to first-line thiazide prescribing.

Interpretation

Changes in prescribing practices occur gradually with the accumulation of small impacts from educational interventions and lay media attention.

Introduction

Most guidelines for treatment of newly diagnosed essential hypertension recommend that a thiazide or a β-blocker should be used first in patients with no major comorbidity,1, 2, 3, 4 though there has been disagreement.⁵ These guidelines apply especially to patients over age 65 because thiazides have been shown to lower not only coronary and stroke mortality and morbidity, but total mortality as well.⁶ Only if there is a contraindication to diuretics or β-blockers should inhibitors of angiotensin-converting enzyme (ACE) or calcium-channel blockers (CCB) be prescribed;1, 2, 7, 8 neither ACE inhibitors nor CCBs have been studied optimally in trials designed to measure changes in morbidity or mortality associated with hypertension treatment.

Despite these guidelines in the USA, thiazides and β-blockers accounted for only 40% of the total prescriptions for hypertension in 1995, down from 70% in 1986.⁹ Similarly, in British Columbia, Canada, in 1995, thiazides and β-blockers accounted for 36% of claims for antihypertensive drugs among elderly people (unpublished data).

This discrepancy between guidelines and practice poses a challenging question to educators of physicians: how does evidence influence physician prescribing? Publication of results of clinical trials correlates with changes in physician behaviours¹⁰ but the mechanisms are not well understood. Recent systematic reviews from the Cochrane Library of the few relevant studies show that the impact of printed educational materials on the behaviour of health-care professionals is negligible and of uncertain clinical importance.¹¹ The reviews also show that audit and feedback are sometimes effective, particularly with prescribing and diagnostic tests, but the effects are small to moderate.¹² The use of local opinion leaders has produced mixed results.¹³ Some evidence exists that alarming medical news and warnings to the general public can influence medication use and sequelae measurably, either appropriately (such as the reports on aspirin use and Reye's syndrome¹⁴) or inappropriately (third-generation oral contraceptives and abortions¹⁵). More studies like these are needed to elucidate the role of lay media and educational interventions.

The years 1994–96 provided a natural experiment. In March and September, 1995, US and Canadian lay media gave widespread news coverage to a US case-control study,16, 17 which showed that taking CCBs for hypertension had higher rates of myocardial infarction than patients taking thiazides or β-blockers. Although the study was not definitive, headlines such as “Blood-pressure drugs feared bad for hearts”¹⁸ suggested otherwise. Medical news media geared towards medical professionals, and lay health magazines and newsletters, picked up the story in the following months and referred to it again when covering later scientific reports on CCBs that suggested risks of gastrointestinal haemorrhage,¹⁹ total mortality,²⁰ cancer,21, 22 and vascular events²³ were higher in patients on CCBs than on other antihypertensive drugs.

Also during 1994–96, the Therapeutics Initiative, an organisation at the University of British Columbia dedicated to evidence-based drug assessment and education, distributed newsletters to all actively prescribing physicians in the area, and conducted a teleconference and a series of small group workshops. Each of these educational interventions promoted awareness of the scientific evidence favouring the use of thiazides and β-blockers over CCBs and ACE inhibitors for first-line prescribing.