Complete antibiotic coverage used mostly for polymicrobial infections

Future studies should determine if this is the best approach, researchers said

Andrea Lobo, PhD avatar

by Andrea Lobo, PhD |

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Pulmonary exacerbations in children with cystic fibrosis (CF) caused by multiple bacteria (polymicrobial) are generally treated with antibiotics that cover all the bacteria detected, a study reported.

Whether this strategy is associated with better clinical outcomes than using antibiotics that cover only some of the detected bacteria remains to be established and should be addressed in future studies.

The study “represents a necessary step toward a standardized antibiotic selection to treat pulmonary exacerbations in children with CF,” the researchers wrote in “Polymicrobial infections and antibiotic treatment patterns for cystic fibrosis pulmonary exacerbations,” which was published in the Journal of Cystic Fibrosis.

Pulmonary exacerbations refer to the acute worsening of lung symptoms and are associated with reduced lung function, weight loss, and quality of life. Treating them generally includes clearing the airways and antibiotics. There’s much variability in the antibiotics prescribed, however, and CF Foundation guidelines don’t provide evidence-based recommendations on selecting antibiotics.

For patients with pulmonary infections caused by two or more CF-related bacteria, it’s unclear which antibiotic regimen should be adopted.

“Studies evaluating the use of antibiotics in the care of [people with CF] are needed to maximize antibiotic-related benefits while minimizing the risk of adverse effects,” wrote the researchers in the U.S., who used the CF Foundation Patient Registry-Pediatric Health Information System to describe practices about antibiotic use in children with CF who had two or more CF-related bacteria in the year before their hospitalization to treat a pulmonary exacerbation.

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Treating pulmonary exacerbations with antibiotics

In total, 4,923 children (median age, 14.8) treated between 2006 and 2019 were included. They had a total of 27,669 pulmonary exacerbation episodes.

Nearly three-quarters of all exacerbations (20,214, 73%) had polymicrobial infections (caused by combinations of CF-related bacteria), the most common being Pseudomonas aeruginosa and methicillin-resistant Staphylococcus aureus (MRSA). The second most common were P. aeruginosa and methicillin-sensitive Staphylococcus aureus (MSSA).

A quarter of the exacerbations were caused by one CF-related bacterium (6,824), and 2% (631) had no bacteria detected in the previous 12 months.

Complete antibiotic coverage was seen in 93% of pulmonary exacerbations with one CF-related bacterium and in 68% of polymicrobial exacerbations. In the study, complete antibiotic coverage was defined as being prescribed one or more intravenous, inhaled and/or oral antibiotics with predicted activity against all CF-related bacteria detected.

Complete antibiotic coverage depended on the specific CF-related bacteria detected. For instance, if P. aeruginosa, MSSA, and/or Burkholderia cepacia complex species were present, the complete coverage was 90% or higher. Coverage for Haemophilus inflluenzae was 83%, and for MRSA 82%. The percentage was lower for Stenotrophomonas maltophilia (69%) and Achromobacter xylosoxidans (53%).

“These results suggest that providers may be attributing greater importance to certain bacterial species when prescribing various antibiotics and antibiotic combinations to target an individual CF-related bacteria in order of some priority, such as perceived pathogenicity [the ability to cause disease] or contribution to that [pulmonary exacerbation], as well as concerns of antibiotic toxicity or known allergies,” the scientists wrote.

Also, a pulmonary exacerbation treated with complete antibiotic coverage was more likely to occur when a previous exacerbation had complete coverage. An exacerbation was 3.48 times more likely to have complete coverage for MRSA if a previous exacerbation with complete coverage for MRSA occurred.

A pulmonary exacerbation was less likely to have complete coverage, however, if it had been previously treated with partial antibiotic coverage — a prescription that doesn’t cover all CF-related bacteria detected.

The prescribing patterns differed according to region. For example, in the West, complete antibiotic coverage was less likely than in the South for MRSA and MSSA, and more likely for A. xylosoxidans.

“However, overall no clear regional patterns in antibiotic coverage were identified across the different CF-related bacteria,” the researchers noted.

Age and lung function at the study’s start were not significantly associated with antibiotic selection. Hispanic ethnicity correlated with a higher likelihood of partial MRSA antibiotic coverage.

“Future studies are needed to better evaluate clinical outcomes among polymicrobial pulmonary exacerbations from [people with CF] treated with complete versus partial antibiotic coverage,” the researchers wrote.

A separate study in children by the same research team found treating pulmonary exacerbations with antibiotics covering both MRSA and P. aeruginosa didn’t improve outcomes compared with targeting Pseudomonas alone.

“If similar results were found in studies comparing other CF-related bacteria combinations, it might be possible to limit the breadth and burden of antibiotics administered to these children with CF,” the researchers wrote.