Doxycycline Looks to Be Acceptable Alternate Treatment for Syphilis in HIV-Positive Patients

The incidence of sexually-transmitted diseases (STDs) continues to climb in the United States, with the Centers for Disease Control and Prevention (CDC) reporting that the 3 nationally reported STDs—chlamydia, gonorrhea, and syphilis—were at the highest numbers ever—more than 2 million cases—in 2016. Although the majority of these new diagnoses were chlamydia (1.6 million), cases of primary and secondary syphilis also saw a major increase of 18% from 2015 to 2016. The majority of these new cases occurred among men, particularly gay, bisexual, and other men who have sex with men (MSM).

Treatment for patients with primary, secondary, or early latent syphilis is an intramuscular (IM) injection of 2.4 million units of long-acting Benzathine penicillin G, according to the CDC. For those individuals with late latent syphilis or latent syphilis of unknown duration, the treatment regimen is 3 doses of long-acting Benzathine penicillin G, IM at weekly intervals. Doxycycline can be used as an alternative treatment option to penicillin in some cases, such as in those patients with an allergy to penicillin; however, information on the serologic response after doxycycline in patients who are HIV-positive has been limited.

As such, researchers from the University of São Paulo in São Paulo, Brazil, studied the serologic responses of HIV-positive patients infected with syphilis who were treated with doxycycline and compared these responses with patients who are treated with penicillin. The results of their study were recently presented at the 25th Annual Conference on Retroviruses and Opportunistic Infections (CROI).

For the study, the investigators “analyzed serologic response to syphilis treatment with doxycycline among HIV-infected patients treated during a period of penicillin shortage, and compared [their responses] with treatment response among patients treated with penicillin up to 12 months prior or 6 months after the shortage period,” according to the study abstract. Those cases in which patients were treated with other medication or suboptimal doses, or where patients had neurosyphilis, were excluded from the study.

A total of 61 patients were treated for syphilis with doxycycline from September 2014 to December 2016. Their results were compared with 60 patients who were treated with penicillin. The population of patients treated with doxycycline had a mean age of 49 years (+10 years) while the mean age of the patients treated with penicillin was 45 years (+10 years). The T CD4+ counts for the patients treated with doxycycline were a median of 544 [interquartile range (IQR) 403-694], while those patients treated with penicillin had a median T CD4+ count of 615 (IQR 480-864).

The investigators defined the serologic response to treatment as a “non-reagent venereal disease research laboratory (VDRL) test or a 4-fold or higher reduction in VDRL titers measured 6 to 12 months after treatment.” The results showed that 67% of the patients who were treated with doxycycline (95% CI = 54%-79%) and 68% of the patients (treated with penicillin 95% CI = 55%-80%; P = .895) had a serologic response to treatment.

Based on these results, which showed “no statistically significant difference in serologic response to treatment with either doxycycline or penicillin among HIV-infected patients with syphilis,” the investigators concluded that doxycycline is an acceptable treatment alternative for HIV-positive patients who are infected with syphilis.