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 monohydrate, is effective for treating bacterial cellulitis but has not been recommended or studied for treating Lyme disease because of poor in vitro activity. Objective: To describe the outcome of patients with EM who were treated with cephalexin. Patients and Methods: Patients presenting with EM to the Lyme Disease Diagnostic Center in Westchester, NY (May 1992-September 1997). A 2-mm punch biopsy 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 with cephalexin prior to our evaluation; 9 (82%) were originally diagnosed with cellulitis. Cephalexin was administered for 8.6 days (range, 2-21 days) prior to presentation. All 11 patients had clinical evidence of disease progression, including 8 whose rash enlarged, 2 who developed seventh-nerve palsy (1 with new EM lesions), and 1 who developed new EM lesions. Borrelia burgdorferi grew in cultures from 5 patients despite a mean of 9.8 days of treatment with cephalexin (range, 5-21 days). Conclusion: Cephalexin should not be used to treat early Lyme disease and should be prescribed with caution during the summer months for patients believed to have cellulitis in locations where Lyme disease is endemic.