A 16-year-old male who has sex with men presents to a gastroenterologist with a 4-week history of rectal pain, discharge, and tenesmus, which has been mistaken for inflammatory bowel disease. A nucleic acid amplification test from a rectal swab is positive for Chlamydia trachomatis. Given the high index of suspicion for lymphogranuloma venereum (LGV) proctocolitis, what is the most appropriate treatment regimen?