Unexplained reduced microbiological efficacy of intramuscular benzathine penicillin G and of oral penicillin V in eradication of group a streptococci from children with acute pharyngitis.

To evaluate the efficacy of oral penicillin V and intramuscular benzathine penicillin G (BPG) in eradicating group A streptococci from the upper respiratory tract. Two randomized, single-blind, multicenter antibiotic efficacy trials in children using recommended doses of either oral penicillin V or intramuscular BPG for treatment of acute-onset pharyngitis associated with isolation of group A streptococci were conducted. Throat examinations and cultures were obtained at enrollment and on days 5 to 8, 10 to 14, and 29 to 31. Thirty-five percent of 284 evaluable patients treated with oral penicillin V and 37% of BPG-treated patients were microbiologic treatment failures at either 10 to 14 or 29 to 31 days. Although these findings do not provide sufficient evidence to change current treatment recommendations or public health policy, important questions are raised about currently recommended penicillin doses, about the role of the carrier state, and possibly about adequate bioavailability of intramuscular BPG. These findings require confirmation.