Here's a man speaking sense. 💯
Except, I highly doubt that 65% figure you are saying. I don't see how those bacteria could get into the body while taking doxycycline, especially since it treats syphilis and gonorrhea even after you been infected.
It's also an anti-malarial, for goodness sake. Doesn't it stop virtually 100% of malaria infections when taken as prescribed by a doctor?
I don't see how any bacterial STD is getting into you with doxy in your system. It prevents life in most organisms.
That said, I still don't see the sense in using it as PEP when you could just simply treat an infection after you get it, rather than endlessly take antibiotics.