Hello. Thank you writing to us at healthcaremagic Chlamydia is a common cause of Non-Gonococcal urethritis (NGU) and a week of doxycycline is usually enough in most cases. Persons who have persistent urethritis can be retreated with the initial regimen only if they did not comply with the treatment regimen or if they were re-exposed to an untreated sex partner. In unresponsive cases, other organisms may be responsible for NGU like herpes, Trichomonas genitalium, adenovirus, mycoplasma and ureaplasma etc Organisms like Ureaplasma and mycoplasma respond better to Azithromycin as they might be doxycycline resistant. Therefore Azithromycin is usually preferred over doxycycline if NGU requires a retreatment. Trichomonas can also be a cause of urethritis and should be treated with single dose of metronidazole in those cases who have persistent urethritis. I suggest that you visit your sexual health specialist if your problems are persisting even after a repeat course of oral antibiotics. It is important to treat possible partner co-infection and avoiding sexual activity with partner for a week. Regards