The best antibiotic for secondary prophylaxis is benzathine penicillin G (1.2 million units, or 600,000 units if 27 kg) delivered every 4 weeks. It can be given every 3 weeks, or even every 2 weeks, to persons considered to be at paicularly high risk. Oral penicillin V (250 mg) can be given twice-daily instead but is somewhat less effective than benzathine penicillin G. Penicillin allergic patients can receive erythromycin (250 mg) twice daily. Ref: Carapetis J.R. (2012). Chapter 322. Acute Rheumatic Fever. In D.L. Longo, A.S. Fauci, D.L. Kasper, S.L. Hauser, J.L. Jameson, J. Loscalzo (Eds), Harrison's Principles of Internal Medicine, 18.