Lyme arthritis in the knee is treated with which antibiotic?

• A. Doxycycline
• B. IV Ceftriaxone
• C. Amoxicillin
• D. Azithromycin

Answer: (A)

Lyme arthritis in the knee is caused by Borrelia burgdorferi, and treating it effectively requires an antibiotic that both targets the organism and penetrates joint tissue well. Doxycycline fits best because it is active against Borrelia, concentrates effectively in synovial fluid, and is easily given orally for about four weeks, making it a convenient and usually first-line option for adults without pregnancy or under-8 restrictions.

Intravenous ceftriaxone is typically reserved for cases with neurologic involvement or when there’s failure to respond to oral therapy. Amoxicillin can be used as an alternative, but it’s less convenient. Azithromycin is not reliably effective against Borrelia and is generally avoided. Thus, doxycycline stands out as the best initial treatment for knee Lyme arthritis in appropriate patients.