Macrolides are a group of antibiotics found in bacteria called streptomycetes. They help the body fight bacterial infections. People with cystic fibrosis (CF) may be prescribed macrolides for a long period of time to treat lung infections on an ongoing basis. Their importance in CF is related to the drug’s ability to disrupt Pseudomonas aeruginosa’s connection to cells in the body. Macrolide-based antibiotics include erythromycin, clarithromycin and azithromycin.

History of macrolides

Macrolides were discovered in the 1950s when scientists isolated erythromycin from the soil bacterium Streptomyces erythaeus. Later, in the 1970s and 1980s, synthetic macrolides were developed (clarithromycin and azithromycin).

How macrolides work

Macrolides are natural lactones with a large ring of 14 to 20 atoms. They bind to the 50S subunit of the bacterial ribosome and stop bacterial protein synthesis. Their action is primarily bacteriostatic (they stop the growth of bacteria) but may also be bactericidal (killing bacteria) when administered in high concentrations.

Studies of macrolide use have shown a modest improvement in lung function, weight gain, and fewer lung exacerbations.Figure: erythromycin structure.

Other details about macrolides

Erythromycin, clarithromycin, and azithromycin are taken by mouth or intravenously. Common side effects are gastrointestinal disorders such as an upset stomach, diarrhea, vomiting and loss of appetite and headache.

CF Foundation guidelines recommend long-term azithromycin for people with CF older than 6 who are chronically infected with Pseudomonas aeruginosa, who weigh more than 53 pounds and with an FEV1 (a measure of lung function) greater than 30 percent.

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