Hi, Markus,
I don't have experience with metronidazole for Lyme, but I definitely identify with your desire to be cautious and manage the risks of your treatment. As I understand it, many medications are toxic to humans in the long term. I've read innumerable times that long-term antibiotic usage is linked to increased risk of all types of cancers. But of course sometimes antibiotics save lives! Dr. Rawls calls these "heroic therapies," things that help but you have to hope they harm the bug more than they harm the good stuff. (Scroll down for a descript
ion of heroic therapies https://rawlsmd.com/health-articles/my-chronic-lyme-disease-journey)
Have you discussed this with your prescriber? In my opinion (and I say this often on here, so please forgive the repetition) a good LLMD should be well-versed in multiple types of treatment when it comes to Lyme, not just pharmaceuticals, since so many of us have allergies, concerns, etc. and require integrative treatment. I hope your doc is responsive and helpful in finding a treatment program that feels comfortable to you!
Hope you get responses more geared toward your actual question.