Introduction British Association for Sexual Health and HIV (BASHH) and Australian guidelines recommend either azithromycin or doxycycline for the treatment of rectal chlamydia. We investigated treatment efficacy of two treatments for rectal chlamydial infection.

Method A retrospective cohort of male and female patients diagnosed with rectal chlamydial infection between 2009 and 2015 was created at the STI services (Clinic 275) in Adelaide, Australia. Patients were included in the analysis if they were treated with azithromycin (1 g single dose) or doxycycline (100 mg twice a day for 10 days) and returned for repeat testing 14 to 180 days after treatment commenced. Log binomial models were used to estimate the relative risk (RR) of recurrent rectal chlamydia associated with the treatment with azithromycin versus doxycycline.

Results Of 526 patients diagnosed with rectal chlamydial infections over the study period, 73% (n=384) were men and 27% (n=142) were women; 419 (79.7%), 93 (17.7%) and 14 (2.6%) patients were treated with doxycycline, azithromycin or other medication respectively. Of these patients, 173 (41.3%) of 419 doxycycline-treated patients and 31 (33.3%) of 93 azithromycin-treated patients were retested between 14 and 180 days after treatment commenced (p=0.16). Among these patients, the repeat rectal chlamydia test was less commonly positive in those treated with doxycycline (5.8%; 95% Confidence Interval (CI) 0.03–0.10) compared with those treated with azithromycin (19.4%; 95% CI 0.09–0.36) and (p=0.01). In the multivariate analysis, azithromycin-treated patients had a significant higher risk of a positive test in the 14 and 180 days after treatment commenced (adjusted relative risk (aRR) 2.78, 95% CI 1.10–7.05).

Conclusion The findings suggest that doxycycline may be more effective than azithromycin in treating rectal chlamydial infection.