SAN DIEGO, CA—Among Medicare beneficiaries diagnosed with acute myocardial infarction (AMI), filling a prescription for an antimicrobial was positively associated with an adverse cardiac event within the week, a study presented at IDWeek 2015 has found.

However, what is not clear is whether “antimicrobials themselves or the conditions they were meant to treat are the cause of these adverse events,” reported Linnea Polgreen, PhD, Pharmacy Practice & Science, University of Iowa, College of Pharmacy, Iowa City, Iowa.

In healthy populations, studies have associated antimicrobials—especially the macrolides—with negative cardiac outcomes. How then, does a high-risk population, older patients with AMI, fare? To answer that question, Dr. Polgreen and her colleagues “constructed a cohort of 185,010 Medicare beneficiaries diagnosed with an AMI” and followed them for 1 year after their index AMI.

“For each week a patient was followed, we determined whether a patient suffered another AMI, any arrhythmias, or any important cardiac event,” she noted. Also determined was if a prescription was filled for a macrolide (eg, azithromycin, clarithromycin), a fluoroquinolone (eg, levofloxacin, moxifloxacin), a penicillin (eg, amoxicillin-clavulanate), or a tetracycline (eg, doxycycline) antibiotic.

A logistic regression model of scenarios including the 4 cardiac outcomes and the 6 antimicrobials, used antimicrobial prescription in a week as the main independent variable, with the dependent variable being a cardiac event in the following week. Patient comorbidities, medications, procedures, demographics, and insurance status were included in each of the models.

“For almost all models, an antimicrobial prescribed in the previous week was positively associated with the cardiac events studied,” Dr. Polgreen stated. “Clarithromycin was not associated with ventricular arrhythmia, and doxycycline was not associated with AMI or ventricular arrhythmia.”

After adjusting for over 100 covariates, “the odds ratio became considerably smaller in nearly every model.” None of the antimicrobials were associated with ventricular arrhythmias, and 3 of the antimicrobials—doxycycline, moxifloxacin, amoxicillin-clavulanate—were not significantly linked to any cardiac event.

“Macrolides were significantly associated with AMI, arrhythmias, and any cardiac event but the estimated odds ratios are small, around 1.5—1.8,” Dr. Polgreen concluded. Most of the risk seen from antimicrobials is most likely due to the factors that triggered the prescription, not the actual antimicrobial itself, she noted.