Eucaryotic cells protect Borrelia burgdorferi from the action of penicillin and ceftriaxone but not from the action of doxycycline and erythromycin.

Despite appropriate antibiotic treatment, Lyme disease patients may have relapses or may develop chronic manifestations. The intracellular location of Borrelia burgdorferi suggests that antibiotics that penetrate cells will have greater efficiency. Doxycycline or erythromycin was more effective than penicillin or ceftriaxone in killing B. burgdorferi when the organism was grown in the presence of eucaryotic cells.