Acute rheumatic fever (ARF) is an autoimmune condition caused by untreated group A streptococcal (GAS) infection of the throat and possibly skin. Multiple or severe attacks of ARF can cause permanent heart damage known as rheumatic heart disease (RHD). Painful monthly injections of Benzathine Penicillin G (BPG) are given intramuscularly for 10 years to prevent GAS infections that can lead to ARF and cause RHD. A reformulated BPG is desperately needed. Early studies determining how BPG worked in humans were carried out in healthy, fit, young military recruits who did not have ARF/RHD. This project seeks to determine the pharmacokinetic characteristics of BPG in a paediatric population of predominantly Pasifika and Maori children, currently receiving monthly injections of BPG. This is a prospective cohort study where each participant will contribute finger prick blood samples for dried blood spot (DBS) assay measures for penicillin G and Anti-Streptolysin-O titres (ASOT) blood levels.