In a clinical trial involving HIV-negative volunteers with early-stage syphilis, researchers have found that antibiotic pills (azithromycin) are as effective as penicillin injections in curing early-stage syphilis. The study was supported by the National Institute of Allergy and Infectious Diseases, part of the National Institutes of Health.
Edward W. Hook, III, M.D., of the University of Alabama at Birmingham, led the trial. Between June 2000 and March 2007, HIV-negative volunteers aged 18 to 55 enrolled at eight sites in the United States and Madagascar. Volunteers were randomly assigned to receive either two injections of benzathine penicillin G or four tablets of the broad-spectrum antimicrobial macrolide drug azithromycin. Of 517 total enrollees, 469 were included in an intention-to-treat analysis. Among azithromycin recipients, 77.6 percent (180 out of 232) were cured of syphilis, while cure rate among penicillin recipients was 78.5 percent (186 out of 237).
Although long-acting penicillin delivered by injection is recommended as the preferred treatment for early syphilis, the authors note that this therapy has shortcomings, particularly in resource-limited settings. Penicillin injections can cause allergic reactions, and the drug must be refrigerated and administrated by trained personnel. The orally administered azithromycin may provide a good alternative for treating HIV-negative people with early-stage syphilis, the scientists conclude. They note that there is a potential for syphilis-causing bacteria to acquire resistance to macrolide drugs such as azithromycin and they recommend continued research into this possibility.
Detailed information about the study's design is available at clinicaltrials.gov.
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EW Hook et al. A phase III equivalence trial of azithromycin versus benzathine penicillin for treatment of early syphilis. Journal of Infectious Diseases DOI: 10.1086/652239 (2010).