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Rifalazil May Have Advantages Over Azithromycin for Treating Nongonococcal Urethritis, Chlamydia: Presented at ICAAC

By Paula Moyer

WASHINGTON, DC -- November 3, 2004 -– Patients with nongonococcal urethritis (NGU) and chlamydia may have a more robust response to the novel antibiotic rifalazil than to the standard treatment, azithromycin (Zithromax), say researchers.

"We saw a very promising response to this single-dose treatment," said investigator Andrew Sternlicht, MD. "We hope that it will broaden the treatment options for this condition and still retain the convenience of existing treatments." Dr. Sternlicht, who made the presentation here October 31st at the 44th Interscience Conference on Antimicrobial Agents and Chemotherapy, is the vice-president of clinical research at ActivBiotics, based in Lexington, Massachusetts, which manufactures rifalazil and which sponsored the study.

In this double-blind, randomized trial, the investigators compared the effect of rifalazil and azithromycin for the treatment of NGU and chlamydial infection. Of 111 patients with NGU who were recruited to the study and clinically evaluable, 76 were microbiologically evaluable. The patients were all male, aged 18 to 45 years old.

The researchers were interested in the potential of rifalazil, a novel rifamycin, in this setting because of its potent bactericidal activity and prolonged half-life, more than 100 hours, as well as its promising intracellular penetration (> 300:1). The subjects had acute NGU and were also tested for chlamydia. Clinical and microbiologic responses were compared for single doses of rifalazil at 2, 5, 12.5, and 25 mg. Azithromycin was administered at the standard dose of 1 g. The study points were 2 and 5 weeks after treatment.

The investigators documented a clinical dose response for 86% of rifalazil patients who received the 25 mg dose at 2 weeks and 59% at 5 weeks (P =.001 and P =.049 compared to baseline, respectively). Among these patients, 85% had a documentable microbiologic dose response at 2 weeks and 83% had this response at 5 weeks (P =.005 and P =.007 compared to baseline). In the azithromycin group, the clinical cure rate was 77% at 2 weeks and 63% at 5 weeks. These patients' microbiologic cure rates were 83% at 2 weeks and 64% at 5 weeks.

The composite endpoint of therapeutic cure, consisting of both clinical and microbiologic cure at 2 weeks was 85% for patients in the rifalazil 25 mg group, compared to 58% of those in the azithromycin group. Adverse events were mild to moderate and occurred in 23% of rifalazil patients and 24% of azithromycin patients. The most commonly reported adverse effects were headache in the rifalazil group, in 14% of patients, and gastrointestinal symptoms in the azithromycin group, in 12% of patients. AZI patients most commonly reported gastrointestinal symptoms (12%).

[Presentation title: A Double-Blind, Randomized Trial of Rifalazil (RFZ) for the Treatment of Nongonococcal Urethritis (NGU) and Chlamydial Infection. Abstract L-992b]

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