MEDICATIONS: DRUG RESISTANT PNEUMOCOCCAL BACTERIA INCREASING AS ANTIBIOTIC USE GROWS

October 16, 2001 — As the use of antibiotics known as macrolides increases in the United States, drug resistant strains of Streptococcus pneumoniae (a bacteria that commonly causes pneumonia) have become more common, according to an article in the October 17 issue of The Journal of the American Medical Association.

Terri B. Hyde, M.D., of the Centers for Disease Control and Prevention in Atlanta, and colleagues with the Active Bacterial Core Surveillance/Emerging Infections Program Network examined resistance to macrolide antibiotics among Streptococcus pneumoniae bacteria, the most common cause of community-acquired pneumonia.

Macrolides are a class of antibiotics that include erythromycin, clarithromycin and azithromycin. According to background information cited in the article, macrolides are recommended as first-line therapy for adults with community-acquired pneumonia in the United States and Canada. The newer macrolides are popular because of convenient dosing schedules and fewer adverse effects. Although macrolide resistance among S pneumoniae is increasing in the United States., it is unknown whether resistance is a significant problem or whether macrolides remain useful for treatment of the most resistant strains.

The authors analyzed data on 15,481 isolates (pure microbial strains separated from a mixed laboratory culture) from bacterial cultures from invasive S. pneumoniae infection (such as meningitis or bloodstream infection) collected by the CDC's Active Bacterial Core surveillance system in eight states. They focused on trends in macrolide use and resistance from 1993 to 1999, and the factors associated with resistance.

"From 1993 to 1999, macrolide use increased 13 percent; macrolide use increased 320 percent among children younger than 5 years. Macrolide resistance increased from 10.6 percent in 1995 to 20.4 percent in 1999," the authors report.

"Most resistant strains have MICs [minimum inhibitory concentrations, a measure of the amount of drug necessary to inhibit organism growth, and an indicator of drug resistance] in the range in which treatment failures have been reported," they write.

The authors examined data on two subtypes of the S pneumoniae bacteria — the M phenotype, associated with moderate MICs, and the MLS-B phentoype, associated with high MICs and resistance to the antibiotic clindamycin. "M phenotype isolates increased from 7.4 percent to 16.5 percent, while the proportion with the MLS-B phenotype was stable (3 percent to 4 percent)," they report. "In 1999, M phenotype strains were more often from children than persons 5 years or older (25.2 percent vs. 12.6 percent) and from whites than blacks (19.3 percent vs. 11.2 percent)."

The authors suggest that strategies are needed to control increasing macrolide resistance, especially among children. "Total antibiotic prescriptions have decreased since 1993 among all age groups, but our data show that macrolide prescriptions have increased dramatically in children," they write. "Given the high proportion of macrolide-resistant pneumococci among the pediatric population, decreasing inappropriate antibiotic use, especially with macrolides, is important to the success of strategies that will reduce macrolide resistance."

"Pneumococci are again showing their remarkable ability to adapt to their environment, and it remains our challenge to utilize macrolides and other antibiotic agents appropriately and promote rapid introduction of effective pneumococcal vaccines," they conclude.