The impact of clinical trials on the use of medications for acute myocardial infarction. Results of a community-based study.

Background: The impact of clinical trials on medical practice remains controversial, in part because of weak study designs and nonrepresentative study samples.

Objective: To assess changes in trends in medication use in the setting of acute myocardial infarction (AMI) before and after publication of two large clinical trials: the Second International Study of Infarct Survival (ISIS-2) trial that supported the use of aspirin after AMI and the Multi-center Diltiazem Postinfarction Trial that reported no overall benefit from the use of calcium antagonists after AMI.

Methods: Study patients consisted of 2114 patients hospitalized with AMI in 16 hospitals in metropolitan Worcester, Mass, during 1986, 1988, and 1990. Data were obtained from medical records. We used multivariable logistic regression models to examine the rate of change in the use of selected medications before and after trial publication, controlling for medical history, characteristics and complications of AMI, medications taken, and procedures performed during hospitalization. The dependent variable was receipt of the specific medication under investigation.

Results: Before publication of ISIS-2, 26% of patients with AMI received aspirin while hospitalized compared with 66% after its publication. However, in-hospital aspirin use began to rise before ISIS-2 with an immediate increase in the level of use occurring after trial publication but with no significant change in the rate of increase. Before publication of the Multicenter Diltiazem Postinfarction Trial, 57% of patients with AMI were new recipients of calcium antagonists compared with 51% after trial publication. The decrease in calcium antagonist use began after trial publication (odds ratio, 0.79 per 6-month period; 95% confidence interval, 0.71 to 0.88).

Conclusions: The published results of large trials of cardiovascular therapies have had variable impact on medication use. Efforts to assess the effects of publication of new scientific information on medical care need to consider prior trends in treatment patterns and the varying contexts of medical care. They should consider both direct and indirect routes of influence.