Introduction Guidelines for the treatment of early syphilis recommend benzathine penicillin G (BPG) for all patients regardless of HIV status. Concerns of HIV-positive patients developing asymptomatic neurosyphilis have prompted some to prescribe a neuropenetrative regimen of procaine penicillin (PP) with probenecid. There is heterogeneity in prescribing and the debate surrounding this issue is amplified by the global probenecid shortage. One centre in the UK has historically treated patients with PP regardless of syphilis stage. We compared serological response, adherence and tolerance among these patients compared with those receiving alternative regimens.

Methods A retrospective analysis of HIV positive individuals with early syphilis infection. Response to treatment was defined by ≥4-fold decline in VDRL titer within 13 months.

Results 197 patients were diagnosed with primary(24%), secondary(50%) or early- latent(26%) syphilis between 2012-2015. 102(52%) received PP, 26(13%) BPG, 38(19%) doxycycline for 28 days and 4(2%) amoxicillin plus probenecid. For 27(14%), treatment regimen was unknown. Of those who completed PP, 91% had serological response, BPG 65%, doxycycline 79%. Four patients on PP switched due to non-adherence. Of the PP patients median age 42, CD4 576 and 80% were on antiretroviral therapy. This did not differ greatly between those who achieved serological response and those who did not.

Discussion We demonstrate good adherence and tolerance of PP. There was a superior serological response to treatment in this group but a large loss to follow up among those treated with BPG. Further statistical analysis may identify factors associated with serological failure. Prospective studies exploring co-infection are required.