Figures show Pacific and Māori children and young adults have the highest rates of rheumatic fever in New Zealand.
Victoria University's Dianne Sika-Paotonu and her fellow researchers will investigate how penicillin treatment has been working across different populations.
The initial studies were carried out on US soldiers in the 1950s.
Dr Sika-Paotonu has been awarded an extra 170-thousand US dollars to look into the issue.
She said it was clear better information was needed on how the drug works
"The initial studies around BPG (Benzathine Penicillin G) were carried out in the 1950s," said Dr Sika-Paotonu.
"The injections were given to United States' soldiers who were all fit, healthy, Caucasian men aged between 18 and 24, and who had never had rheumatic fever.
"The data about how their bodies processed BPG were used to determine how we use the penicillin for rheumatic fever."
The project involves a team of Victoria University researchers collaborating with health and medical research organisations in New Zealand, Australia and the United States
Photo: RNZ Daniela Maoate-Cox Practice Nurse Litia Gibson says reducing rates of rheumatic fever is often opportunistic work involving testing entire families when just one member is ill.