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Zithromax Not a Sure Bet for Curing Syphilis

Researchers urge caution in using the oral antibiotic

WEDNESDAY, July 7, 2004 (HealthDayNews) -- Doctors increasingly rely on an oral antibiotic called Zithromax to treat patients with syphilis instead of the traditional therapy -- two painful injections of penicillin G benzathine in the buttocks.

But a report in the June 8 issue of the New England Journal of Medicine suggests the newer therapy, referred to by its generic name azithromycin, may not always work.

"The basic message of this paper is that this particular drug, azithromycin, which is being used by an increasing number of clinicians to treat syphilis, may not be the best choice," said study author Sheila A. Lukehart, a research professor of medicine at the University of Washington in Seattle.

Dr. Edward W. Hook III, an infectious diseases expert at the University of Alabama at Birmingham, said further study is needed but agreed the new research sounds an important cautionary note.

"Haphazard, uncontrolled use of azithromycin should not be carried out unless complete and careful follow-up can be conducted," he said.

While azithromycin is not currently recommended by the U.S. Centers for Disease Control and Prevention for treating syphilis, the medication caught hold among clinicians as a convenient and effective alternative to traditional therapy.

"They're using it [azythromycin] because the currently recommended drug, benzathine penicillin, is not a pleasant drug to give or get," Lukehart explained. "It's a very large volume, it's thick, it's painful to receive."

Syphilis is a sexually transmitted disease caused by the bacterium Treponema pallidum. These days, it is particularly rampant in gay men, many of whom are HIV-infected.

Health officials in the United States reported more than 32,000 syphilis cases in 2002, according to the CDC's National Center for HIV, STD and TB Prevention. That figure includes 6,862 cases of primary and secondary syphilis.

In its primary stage, syphilis is characterized by a single sore or multiple sores on a person's penis, vagina, anus or mouth. If it isn't treated early or adequately, it can lead to a secondary stage, marked by a rash on one or more parts of the body. Other signs of secondary syphilis may include fever, swollen lymph glands, sore throat, patchy hair loss, headaches, weight loss, muscle aches and fatigue.

Without treatment, the infection remains in the body, even if the person has no symptoms. Late-stage syphilis can damage the internal organs, leading to difficulty coordinating muscle movements, paralysis, numbness, gradual blindness, dementia or even death.

Penicillin remains the treatment of choice for battling syphilis. To date, there have been no documented reports of penicillin-resistant strains of the bacterium T. pallidum.

But is azithromycin as effective as penicillin G benzathine in wiping it out?

Lukehart, who had been collecting samples of the syphilis bacterium for an unrelated study, began to wonder about this after attending a scientific conference with Dr. Jeffrey D. Klausner, director of STD Prevention and Control Services at the San Francisco Department of Public Health and a co-author of the new report.

"He mentioned to me that they had seen a couple of patients that he thought had failed azithromycin therapy for syphilis," Lukehart recounted.

She also recalled earlier research identifying a strain of T. pallidum found to be resistant to erythromycin, an antibiotic in the same class of medications as azithromycin.

Could the genetic mutation that had caused erythromycin resistance be responsible for the apparent failures of azithromycin? Samples of T. pallidum obtained from STD clinics in San Francisco, Seattle, Baltimore and Dublin, Ireland, confirmed the same genetic mutation was present.

The frequency of the mutation among the sampled strains varied from one geographic site to another. In Dublin, 88 percent of the samples contained the mutation. In San Francisco, the proportion of samples containing the mutation jumped from 4 percent in 1999 to 37 percent in 2003.

Either a strain of T. pallidum has gotten into a population where it is spreading or there is some pressure that is encouraging selected strains to survive, Lukehart explained.

On the other hand, Lukehart's study describes patients who were discovered because they were not doing well on azithromycin, Hook noted. It's unclear how many people in the four cities were treated successfully.

An ongoing trial sponsored by the National Institute of Allergy and Infectious Diseases comparing azithromycin with benzathine penicillin for early syphilis treatment should provide some answers, he said.

"If the results of that analysis had shown a significant increased treatment failure rate in patients treated with azithromycin, this study would have been halted," Hook added.

More information

The American Social Health Association has more about syphilis.

SOURCES: Sheila A. Lukehart, Ph.D., research professor, medicine, Division of Allergy and Infectious Diseases, University of Washington, Seattle; Edward W. Hook III, M.D., professor, medicine and epidemiology, University of Alabama at Birmingham, and medical director, STD Control Program, Jefferson County Department of Health, Birmingham, Ala.; National Center for HIV, STD and TB Prevention, Division of Sexually Transmitted Diseases; U.S. Centers for Disease Control and Prevention; July 8, 2004, New England Journal of Medicine
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