Single-Dose Azithromycin Treatment of Incubating Syphilis
abstract & commentary
Synopsis: A single, 1-g dose of azithromycin appeared to prevent the development of syphilis in individuals exposed to this infection.
Source: Hook EW, et al. Azithromycin compared with penicillin G benzathine for treatment of incubating syphilis. Ann Intern Med 1999;131:434-437.
Hook and colleagues randomized 99 patients who had been exposed to infectious syphilis by sexual intercourse in the preceding 30 days to receive either benzathine pencillin G IM or a single, 1-g, oral dose of azithromycin. The majority were exposed to early latent infection. Reasons for exclusion included pregnancy, allergy to study drugs, a past history of syphilis, and a positive RPR and/or FTA-ABS. Twenty-one of 44 (48%) of those assigned penicillin and 12 of 22 (23%) assigned azithromycin treatment proved during follow-up to be nonevaluable (P = 0.01). None of the evaluable subjects (40 azithromycin and 23 penicillin recipients) developed syphilis as determined by RPR and FTA-ABS testing after three months of follow-up. With comparison to an expected rate of infection of 18% based on historical data, the exact binomial confidence intervals for pencillin G benzathine and azithromycin treatments were, respectively, 0.01% to 0.11% (P < 0.001) and 0.01% to 0.17% (P < 0.001).
Comment by stan Deresinski, MD
Between 18% and 58% of individuals sexually exposed to infectious syphilis are reported to develop evidence of infection within 30 days. The currently recommended treatment of choice for incubating and early syphilis is a single 2.4 million unit IM injection of penicillin G benzathine.1 Hook et al conjecture that the much greater drop out rate in the penicillin G benzathine recipients in this study resulted from displeasure resulting from the discomfort of an IM injection. They also point out that public health nurses are often reluctant to administer penicillin in the field. Thus, the availability of a single-dose orally administered non-beta lactam therapy capable of eradicating incubating syphilis represents an important advance. Furthermore, single-dose azithromycin therapy is also effective in the treatment of chancroid, Chlamydia infection, and gonorrhea (al-though a 2-g dose is required for gonorrhea) and is safely used in children and during pregnancy.
As Hook et al point out, a number of factors make the conclusions from this study less than ironclad. The most important of these are the small sample size and the fact that most of the exposures were to partners with early latent syphilis, rather than to more infectious forms. Nonetheless, this study points us in a useful direction.
Reference
1. 1998 Guidelines for treatment of sexually transmitted diseases. MMWR Morb Mortal Wkly Rep 1998;47(RR-1):1-111.
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