Inhaled beta agonists are frequently used in the treatment of chronic obstructive pulmonary disease and asthma. Despite their positive effect on the lungs, these medications may have a negative effect on the heart. The impact of beta agonists on the heart is the opposite of the effect of beta blockers. Preliminary studies have suggested that the use of inhaled beta agonists may have an adverse effect on cardiovascular outcomes. In one previous study, a new prescription for an inhaled beta agonist was associated with a sevenfold increase in the risk of myocardial infarction. Au and associates examined the association between acute coronary syndromes and inhaled beta-agonist therapy.

The data for this study were collected as part of the Ambulatory Care Quality Improvement Project at multiple sites within the Veterans Affairs medical centers. The project was a randomized clinical trial designed to test whether monitoring patients' self-reported health with regular reports to their primary care physicians improved outcomes. Patients admitted to seven different veterans' hospitals with the diagnosis of acute myocardial infarction or unstable angina were included in the study. Study subjects were matched with similar control subjects. Patients who had received a prescription for a beta agonist were identified by electronic pharmacy records. Cardiovascular risk factors were identified from mailed questionnaires and electronic medical records.

Patients who filled a prescription for a beta agonist had an increased risk of acute coronary syndrome compared with patients who had not used beta agonists. This increased risk persisted even after controlling for variables such as age and cardiovascular risk factors. This increase in risk was dose-response–related, with patients having an odds ratio of 1.93 if they filled prescriptions for more than six beta-agonist metered-dose inhalers over a 90-day period. When the use of beta blockers in combination with beta agonists was considered, the risk for acute coronary syndrome did not increase unless the patients had used six or more beta-agonist inhalers. However, those who did not receive beta-blocker therapy had a significantly increased risk for acute coronary syndrome.

The authors conclude that the use of beta-agonist inhalers in the treatment of chronic obstructive pulmonary disease or asthma may increase patients' risk of acute coronary syndrome. While the study does not demonstrate cause and effect, physicians should be cautious when prescribing beta agonists in patients who are at risk for coronary artery disease. Because of the dose-response relationship, if inhaled beta agonists are to be used, the dosage should be monitored and kept to a minimum. In addition, the use of spacers may reduce the oral absorption of inhaled beta agonists and reduce the risk.