Gonorrhea Develops Rapid Resistance to Azithromycin

Emma Hitt, PhD

March 15, 2012

March 15, 2012 — An azithromycin-resistant variant of gonorrhea that developed in just 12 days was detected with genotyping and highlights the rapid emergence of clinical gonococcal resistance, according to a new report.

Olusegun Soge, PhD, from the Neisseria Reference Laboratory at the University of Washington, in Seattle, reported the findings at the 2012 National STD Prevention Conference, held in Minneapolis, Minnesota.

According to Dr. Soge and colleagues, the US Centers for Disease Control and Prevention (CDC) recommends dual therapy with ceftriaxone and azithromycin for the treatment of gonorrhea.

"Although azithromycin has been effective for the treatment of gonorrhea, azithromycin monotherapy is not recommended because of concerns about rapid emergence of macrolide resistance," the authors write.

The report describes the development of resistance to azithromycin in a 26-year-old man with gonococcal urethritis confirmed by culture. The patient received oral azithromycin 2 g but showed persistent symptoms suggestive of treatment failure at follow-up.

The researchers conducted antimicrobial susceptibility testing of pre- and posttreatment isolates using an agar dilution method, according to the Gonococcal Isolate Surveillance Project protocol. Molecular typing was done with Neisseria gonorrhoeae multiantigen sequence typing (NG-MAST) and pulsed-field gel electrophoresis (PFGE).

The 2 isolates had the same NG-MAST results and were indistinguishable with PFGE. They had similar susceptibility patterns, except that the minimum inhibitory concentration for azithromycin increased from 0.5 µg/mL in the pretreatment isolate to 8 µg/mL in the posttreatment isolate.

"Although spontaneous mutants of macrolide-resistant N gonorrhoeae have been successfully selected in the laboratory with in vitro studies, it was intriguing to see the selection of increased azithromycin resistance develop in a patient during treatment with 2 g of azithromycin within 12 days," Dr. Soge told Medscape Medical News.

According to Dr. Soge, this report highlights the utility of antimicrobial susceptibility testing, NG-MAST, and PFGE for investigating treatment failures.

"The emergence and spread of multidrug resistant strains of N gonorrhoeae capable of causing treatment failures could severely jeopardize gonorrhea control efforts," he added.

According to Dr. Soge, clinicians should treat gonorrhea with the CDC-recommended antibiotics: injectable ceftriaxone and either azithromycin or doxycycline.

"It is critical that healthcare providers ask patients treated with azithromycin monotherapy to return within 1 week for a test of cure," he said. "The routine use of azithromycin monotherapy for gonorrhea should be discouraged since, as we saw in this case, azithromycin treatment by itself can rapidly select resistance."

The researchers have disclosed no relevant financial relationships.

2012 National STD Prevention Conference: Presented March 14, 2012.

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