Lack of effectiveness of ofloxacin against experimental syphilis in rabbits.

Ofloxacin, a new pyridone-carboxylic acid derivative, was evaluated in experimental syphilis in rabbits in comparison with penicillin G. Experimental syphilis was established by intradermal injection of Treponema pallidum subsp. pallidum Nichols. Ten days after infection, the dermal lesions were characterized by syphilitic papula accompanied with central necrosis. These animals were subsequently treated either with ofloxacin twice a day at an oral dose of 10 mg/kg or with penicillin G once a day at an intramuscular dose of 10,000 U/kg for 21 consecutive days. In penicillin G-treated animals, the dermal lesions became smaller as early as day 3 of treatment and almost disappeared during the therapy. In marked contrast to remarkable efficacy of penicillin G was further development of the lesions in ofloxacin-treated animals, showing no difference in pathological manifestations as compared to untreated animals. The results of nontreponemal serologic test correlated well with the response of animals to treatment.