How long does it take before syphilis rash on back goes away? was diagnosed with neuropsyphilis and iv therapy of penicillin has been completed.

Should have cleared: The skin rash of secondary syphilis typically clears up within a few days of starting penicillin. Any rash persisting 10+ days (the usual duration of IV pen for NS) probably wasn't syphilis, and syphilis rash usuallyis body wide, not one area like the back. Maybe penicillin allergy if it started after treatment began. In any case, show it to your doctor. Good luck!