Effectiveness of antimicrobial treatment against Borrelia burgdorferi infection in mice.

Although antimicrobial agents are effective therapy for early Lyme disease, optimal treatment schedules have not been conclusively established. The efficacy of various dosages of eight antibiotics used for borreliosis treatment was evaluated for C3H/HeNCrIBR mice, which reproducibly develop persistent infection, arthritis, and carditis when inoculated with Borrelia burgdorferi. Amoxicillin-clavulanic acid, ceftriaxone, and high-dose penicillin G effectively eliminated infection and disease. Oxytetracycline, doxycycline, chloramphenicol, erythromycin, and azithromycin failed to cure infected mice. There was a correlation between peak serum antibiotic concentrations in mice, as determined by agar well diffusion bioassays, and therapeutic levels in humans. When experimentally inoculated mice were treated at 1 week postinfection with ceftriaxone (16 mg/kg of body weight twice daily for 5 days) and monitored for up to 90 days, all treated mice were free of spirochetes and had no gross or histologic lesions. This antibiotic regimen at days 7 to 11 postinoculation eliminated the spirochetes so that there were no relapses during the 90-day observation period. For experimentally inoculated mice treated with ceftriaxone at 7 or 14 days postinfection, arthritis, carditis, and infection were eliminated. When treatment began at 30 and 90 days after inoculation, infection and active cardiac and arthritic lesions were eradicated; however, residual mild synovitis and vasculitis persisted in some mice. In comparison with inoculated, untreated mice, ceftriaxone therapy at 7, 14, 30, and 90 days postinfection abrogated the development of antibody titers against B. burgdorferi. Having the potential to determine the presence of the spirochete through culture and histologic lesions makes the B. burgdorferi-inoculated C3H mouse model a valuable adjunct in evaluating chemotherapeutic options for Lyme disease.