Natural Experiment of Syphilis Treatment with Doxycycline or Benzathine Penicillin in HIV-infected Patients

Background: Although doxycycline is widely used as an alternative to benzathine penicillin for the treatment of early and late latent syphilis, data on serological response following treatment with doxycycline among HIV-infected patients are limited.

Methods: In this study, we analysed serological response to syphilis treatment with doxycycline among HIV-infected patients treated during a benzathine penicillin shortage period and compared with treatment response among patients treated with benzathine penicillin. Cases with neurosyphilis and those treated with suboptimal doses or with concurrent medications in association with benzathine penicillin or doxycycline were excluded.

Results: Fifty patients treated with doxycycline from September 2014 to December 2016 were compared with 115 patients treated with benzathine penicillin for early, late latent or latent syphilis of unknown duration. Patients treated with doxycycline were slightly older [(median 49 years old, 95% confidence interval (95% CI) 43-56] than those in the penicillin group (median 44 years old, 95% CI 37-50; P = 0.007). Groups had no statistically significant differences regarding sex, HIV suppression under treatment and syphilis stages. Serological response to treatment, defined as a nonreagent Venereal Disease Research Laboratory (VDRL) or at least a four-fold reduction in VDRL titres measured 6-12 months after treatment, was seen in 72% (95% CI 58-84) of patients treated with doxycycline and 70% (95% CI 60-78) of patients treated with penicillin (P = 0.753).

Conclusion: We found no statistically significant differences in serological response to treatment with doxycycline or benzathine penicillin among HIV-infected patients with early, late latent or latent syphilis of unknown duration. Our findings suggest that doxycycline is an acceptable treatment to HIV-infected patients with nontertiary stages of syphilis.