Doxycycline is effective against syphilis; TP is never resistant to the tetracyclines, and doxy (for 2 weeks) is the treatment of choice for early syphilis in persons who cannot safely take penicillin. The effectiveness of a one week course in preventing syphilis has not been studied, but almost certainly would be effective in doing so.
Thanks for replying so quickly.
I was aware that the risk was rather low, although not non-existing.
My GP gave me 14 tabs of 100mg doxy for my on-going throat infection (not related to my kissing cheat). I was told to use them if I do not see any improvement in coming days. I've done some research on pubmed, it looks like doxy is almost as efficient as penicilin for syphilis treatment. Are you aware of any TP doxycycline resistance?
From your experience - if I were recently infected, would a 7 day-course of 100mg doxy be sufficient to clear this fresh infection?
Welcome to the forum.
As for the other STDs you mention, kissing is also very low risk for syphilis. Not zero, but in my four decades in the STD business, I have never seen a case that was not acquired by vaginal, anal, or oral-genital sex. I see no need for testing and certainly not for antibiotic treatment. Just go about your life as normal, without worry.
Of course you could also ask your kissing partner to be tested for syphilis. If you choose this path, do it carefully and diplomatically, to avoid upsetting him or laughing at you (which would be natural reactions among people aware how non-risky this is).
If I were in your situation, I would do none of these things and I would continue unprotected sex with my wife without worrying I could infect her.
I hope this has helped. Best wishes-- HHH, MD