Background: Doxycycline is the preferred recommended second-line agent for the treatment of syphilis, although efficacy data from controlled trials are lacking. We compared the serological responses of patients with early syphilis treated with doxycycline with the responses of patients treated with benzathine penicillin G (BPG).
Methods: All patients who received a diagnosis of early syphilis attending 2 public sexually transmitted disease clinics in Baltimore, Maryland, who were treated with doxycycline (100 mg orally, twice daily for 14 days) between October 1993 and June 2000 were eligible. Patients treated with BPG (a single dose of 2.4 million units intramuscularly) were selected as the control group. Inclusion criteria included a clinician-recorded diagnosis of primary, secondary, or early latent syphilis with reactive serological test results at the time of diagnosis and at least 1 follow-up serological test titer. Serological failure was defined as lack of a 4-fold drop in rapid plasma reagin titer 270-400 days after treatment, or a 4-fold increase in titer 30-400 days after therapy.
Results: During the study period, 1558 patients were treated for early syphilis, and 87 received doxycycline. Of those treated with doxycycline, 34 met the inclusion criteria. Seventy-three patients from a randomly selected group of 200 age-matched individuals treated with BPG met the inclusion criteria. There were 4 patients with serological failure in the BPG group (5.5%; 95% confidence interval [CI], 1.6%-13.8%) and 0 patients with serological failure in the doxycycline group (0%; 95% CI, 0%-10.3%; P=.2). The median times to successful serological responses for patients in the doxycycline and BPG groups were 106 days (95% CI, 75-149 days) and 137 days (95% CI, 111-172 days), respectively (P=.6).
Conclusion: Doxycycline appears to be an effective agent for the treatment of early syphilis.