SAN FRANCISCO — Drug resistance was a common cause of treatment failure in 26 patients with community-acquired pneumonia who developed bacteremia while being treated with macrolide antibiotics, Dr. Gavin Bayan Grant said at the annual Interscience Conference on Antimicrobial Agents and Chemotherapy.
Of the 26 patients who developed bacteremia while on erythromycin, clarithromycin, or azithromycin therapy, 21 (81%) had resistant organisms, compared with 15 (44%) of 34 patients who developed bacteremia after recent use of one of the macrolides (defined as 16–90 days before the bacteremia diagnosis) and 14% of 721 patients who had not been taking any antibiotics and developed bacteremia.
Macrolide antibiotics are standard therapy for outpatient treatment of pneumonia, and evidence that significant macrolide resistance occurs has been inconclusive, said Dr. Grant of the Centers for Disease Control and Prevention, Atlanta. The current findings provide further evidence that resistance can lead to treatment failure with macrolides, which may inform clinical decisions to change antibiotics in some patients, he said at the meeting, sponsored by the American Society for Microbiology.
Dr. Grant has no association with the companies that make macrolides.
After controlling for patient age, immunosuppression, chronic comorbidities, and residence in a long-term care facility, patients failing macrolide therapy were 5 times more likely to have resistant organisms, compared with patients who developed bacteremia after recent macrolide use, and 26 times more likely to have resistance than patients with bacteremia who had not been taking antibiotics.
The study also found that clinicians who define macrolide resistance using a cutoff of a minimum inhibitory concentration (MIC) of at least 16 mcg/mL will miss a significant percentage of the treatment failures. “Failures often occur at macrolide MICs less than 16 mcg/mL,” he said.