Failure of treatment with cephalexin for Lyme disease

Context: Lyme disease typically presents with a skin lesion called erythema migrans (EM), which though often distinctive in appearance may be confused with cellulitis. The first-generation cephalosporin, cephalexin monohydrat e, is effective for treating bacterial cellulitis but has not been recommen ded or studied for treating Lyme disease because of poor in vitro activity. Objective: To describe the outcome of patients with EM who were treated wit h cephalexin. Patients and Methods: Patients presenting with EM to the Lyme Disease Diagn ostic Center in Westchester, NY (May 1992-September 1997). A 2-mm punch bio psy specimen of the leading edge of the EM lesion and/or blood was cultured for Borrelia burgdorferi. Results: Eleven (2.8%) of 393 study patients had been initially treated wit h cephalexin prior to our evaluation; 9 (82%) were originally diagnosed wit h cellulitis. Cephalexin was administered for 8.6 days (range, 2-21 days) p rior to presentation. All 11 patients had clinical evidence of disease prog ression, including 8 whose rash enlarged, 2 who developed seventh-nerve pal sy (1 with new EM lesions), and 1 who developed new EM lesions. Borrelia bu rgdorferi grew in cultures from 5 patients despite a mean of 9.8 days of tr eatment with cephalexin (range, 5-21 days). Conclusion: Cephalexin should not be used to treat early Lyme disease and s hould be prescribed with caution during the summer months for patients beli eved to have cellulitis in locations where Lyme disease is endemic.