Inhibiting ability of benzathine penicillin G towards group A Streptococcus β -hemolyticus in 21 and 28 days after a single intramuscular injection

Background The effectiveness of a single intramuscularbenzathine penicillin G as a secondary prevention of acute rheu-matic fever after 28 days is still controversial. The latest studyshowed that serum penicillin concentration was below protectivelevel in 4 weeks after a single intramuscular injection.Objective This study was a preliminary study to compare the in-hibiting ability of benzathine penicillin G towards group A Strepto-coccus β -hemolyticus in 21 and 28 days after a single IM injectionby using Mueller-Hinton broth method.Methods The inhibiting ability was measured by the serum in-hibitory concentration and serum bactericidal concentration aftera single intramuscular injection of benzathine penicillin G 1.2 mil-lion units.Results The subjects were 28 patients, with mean age of 15.5years (SD 3.4). The numbers of male and female were equal. Meanserum inhibitory concentration in 21 days after a single injectionwas 926.4 (SD 3080.1) and after 28 days was 1540.9 (SD 4275.1),which was not significantly different (p=0.0662). Mean serum bac-tericidal concentration in 21 days after IM injection was 1579.6(SD 4265.7) and in 28 days was 2417 (SD 6849.4) and it was notstatistically different (p=0.2276). Conclusion This study concluded that there was no significant difference in the inhibiting ability of benzathine penicillin G to-wards group A Streptococcus β -hemolyticus between 21 and 28days after a single intramuscular injection