Hello - thanks for asking your question.
To answer your questions:
1) This is not a clear-cut answer. The same bacteria that is sensitive to some antibiotics, may not be to others. Broadly speaking, anaerobic bacteria (bacteroides, clostridium) are more senstive to flagyl, but less so to cipro/doxy/azithro. In some cases there is not enough of the bacteria present in the culture sample to grow, which results in a negative test.
2) A urethral swab test (direct culture of the urethra) can also be performed to identify if bacteria is causing your symptoms.
3) If the bacteria is resistant to other antibiotics, Bactrim may be effective.
4) I am not aware of GI causes cauing urethral symptoms. However, other causes may include a neurological cause (i.e. nerve irritation), or a prostate infection. You may want to consider a neurological evaluation if your physician agrees.
5) If nothing prescription works, I am not aware of anything over the counter that could help. I am also not aware of a country where you can obtain Flagyl without a prescription.
You may want to consider that your symptoms are not caused by an infection. I would consider a cystoscopy to evaluate for urethral strictures or polyps. As I mentioned before, a referral to a neurologist may help.
Followup with your personal physician is essential.
This answer is not intended as and does not substitute for medical advice - the information presented is for patient education only. Please see your personal physician for further evaluation of your individual case.
Thanks,
Kevin, M.D.