In Reply Drs van Brussel and Landman highlight the potential role of probenecid in treating neurosyphilis and note the mechanism by which it enhances penicillin concentrations within the central nervous system. The cited study by Morrison et al1 showed that the combination of amoxicillin with probenecid cured syphilitic orchitis in rabbits. However, the human group in this study provided evidence only that adequate treponemicidal CSF concentrations were achieved with combined amoxicillin-probenecid.
Clement ME, Okeke NL, Hicks CB. Treatment of Late-Stage Syphilis—Reply. JAMA. 2015;313(9):969-970. doi:10.1001/jama.2015.0675