Study: Azithromycin Equal to Penicillin

The oral antibiotic azithromycin is as effective as penicillin injections in curing early-stage syphilis, according to the results of a new study.

"Syphilis remains an important source of morbidity worldwide," wrote Edward W. Hook III, of the University of Alabama-Birmingham and the Jefferson County, Ala., Department of Health, and colleagues. "Long-acting penicillin is the only therapy currently recommended for syphilis in much of the world. Because of hesitation to use penicillin for fear of anaphylaxis, there is a need for an effective, well-tolerated alternative to penicillin for syphilis therapy."

The National Institute of Allergy and Infectious Diseases supported the study, which enrolled 517 HIV-negative participants with early-stage syphilis at eight sites in the United States and Madagascar. All were ages 18 to 55. The volunteers were randomized to receive either azithromycin (2.0 g administered orally as a single dose) or benzathine penicillin G (2.4 million units administered intramuscularly).

After six months of follow-up, serological cure was noted in 180 (77.6 percent) of 232 azithromycin patients and 186 (78.5 percent) of 237 penicillin patients. "Nonserious adverse events were more common among azithromycin recipients than they were among penicillin recipients (61.5 percent vs. 46.3 percent), and such adverse events were accounted for, in large part, by self-limited gastrointestinal complaints," the researchers noted.

"In this trial, the efficacy of azithromycin at a dosage of 2.0 g administered orally was equivalent to that of benzathine penicillin G for the treatment of early syphilis in persons without HIV infection," the authors concluded.

The full report, "A Phase III Equivalence Trial of Azithromycin Versus Benzathine Penicillin for Treatment of Early Syphilis," was published in the Journal of Infectious Diseases (2010;201:1729-1735).

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