[A study of concentration of ampicillin into middle ear effusion after administration of bacampicillin].

We studied the concentration of ampicillin (ABPC) into middle ear effusions after administration of bacampicillin (BAPC). Nine patients with acute purulent otitis media were given orally single doses of the drug at a level of 10 mg/kg, and concentrations of ABPC which is the active antibiotic metabolite of BAPC were determined in middle ear effusions periodically after the administration. Bacteria present in effusions were identified, and their ability to produce beta-lactamase was also determined. ABPC concentrations in middle ear effusions were inversely related to the ability of bacteria detected from the intratympanic cavity to produce beta-lactamase. ABPC concentrations in middle ear effusions from which only beta-lactamase negative organisms were detected were higher by 5.2- and 2.3- fold at 60 and 120 minutes after the administration of BAPC, respectively, than those in effusions from which beta-lactamase positive organisms were detected. ABPC concentrations achieved in middle ear effusions in cases where only beta-lactamase negative organisms were detected exceeded MIC80's of the drug against main causative bacteria of acute purulent otitis media such as Streptococcus pneumoniae, Streptococcus pyogenes, and Haemophilus influenzae. Because only 10% or less of these species produces beta-lactamase, BAPC appears to be one of the highly effective drugs in the treatment of this disease.