AZTREONAM VS GENTAMICIN IN EXPERIMENTAL PERITONITIS AND INTRAABDOMINAL ABSCESS FORMATION

The activity of gentamicin is known to be decreased in acidic environm ents, and both the peritoneum during peritonitis and the interior of a bscesses have been shown to be acidic and hypoxic. The activity of p-l actam antibiotics is felt to be relatively less diminished under the s ame circumstances. We determined that the minimum inhibitory concentra tion of gentamicin against one pathogenic strain of Escherichia coli i ncreased eight-fold, to 8 mu gm/mL, when testing conditions were chang ed from normoxic and neutral to hypoxic and acidic, whereas the MIC of aztreonam doubled under the same conditions, to 0.25 mu gm/mL. In fur ther experiments in a murine model of mixed Escherichia coli/Bacteroid es fragilis intra-abdominal abscesses, we demonstrated that a combinat ion of aztreonam and clindamycin was superior to a combination of gent amicin and clindamycin in terms of completely preventing abscess forma tion (33% vs. 0%) and eliminating Escherichia coli from abscesses that did form (100% vs. 61%).