Because penicillin has a narrower therapeutic index and is less expensive than azithromycin, it is the preferable prophylactic agent. Further, penicillin (250 mg orally twice a day) has a long history of providing safe and effective prophylaxis for rheumatic fever and is the first line oral therapy recommended by the American Heart Association. Thus, penicillin has been chosen as the prophylactic antibiotic in the present study. Blister packs are used to increase compliance and to allow for easier documentation of missed doses.