In a double-blind placebo-controlled trial using triple tetracycline (Deteclo, Lederle) 300 mg twice daily for two weeks in conjunction with metronidazole (Flagyl, May & Baker) 400 mg or matching placebo twice daily for seven days, it was shown that the addition of anti-anaerobic therapy did not significantly affect the number of cases of persistent urethritis or the relapse of patients with non-gonococcal urethritis (NGU).