Well the John Hopkins website, says
"Lyme disease is treatable at all stages, with either oral or intravenous antibiotics. There is some complexity in the treatment decisions, and these differ somewhat for children and adults. There have been few randomized clinical trials of treatment, so optimal choice of antibiotic or optimal duration of treatment are not known. In general, early Lyme disease in adults is treated with doxycycline 100 mg orally twice daily or amoxicillin 500 mg orally three times daily for 20 to 30 days. Doxycycline should not be used in children under age nine years or pregnant women. Other antibiotic choices include phenoxymethyl penicillin, tetracycline, cefuroxime axetil, erythromycin, or azithromycin, with the latter two considered to be second line choices."
"Doxycycline for 30 day courses has been used to treat certain cardiac, nervous system, and joint manifestations of Lyme disease. Other specific manifestations of Lyme disease are generally treated with intravenous antibiotics, most often ceftriaxone 2 gm twice daily for 14 to 30 days, and these include Lyme meningitis, neuroborreliosis, arthritis not responsive to doxycycline, and severe cardiac manifestations."