Reasons why azithromycin 500mg 2 pill did not cure chlamydia?

It depends...: Are you sure it didn't cure? Can't tell by symptoms, only if a test still shows chlamydia. Even then, testing too soon can give false result; retesting shouldn't be done sooner than 3 weeks. Sex with an untreated partner, or a new partner with chlamydia, could seem like treatment failure but really a new infection. Azithromycin works less well in the rectum, from which cervix can be reinfected.