Serum penicillin concentrations after intramuscular administration of benzathine penicillin G in children.

Concentrations of penicillin were measured in serum samples of 26 children who received benzathine penicillin G (BPG) alone or in combination with procaine penicillin (PBPG). Both preparations were well absorbed; peak concentrations of penicillin after PBPG administration were 25-fold larger than those after BPG. One third and one half of serum samples from BPG and PBPG patients, respectively, contained no measurable penicillin activity at 18 days. At 30 days, there was no penicillin activity in any of the samples. These data raise questions regarding the use of BPG and PBPG for prophylaxis of group A streptococcal and pneumococcal infections.