Effect of peritoneal fluid pH on outcome of aminoglycoside treatment of intraabdominal infections.

Netilmicin and clindamycin were administered to 47 patients with an intraabdominal infection who underwent emergency laparotomy. Thirty-one patients were cured, seven were improved, and therapy failed in nine patients despite the fact that all aerobic bacteria isolated from these patients were sensitive to netilmicin as determined by standard in vitro susceptibility tests. The pH of peritoneal and drainage fluid collected intraoperatively and during follow-up correlated with clinical outcome. Acidic pH was found in 21 of 33 (64%) specimens sampled from patients with therapeutic failure compared to 17 of 80 (21%) obtained from the categories "cured" and "improved" (p < 0.001). Netilmicin concentrations in serum or peritoneal/drainage fluid did not correlate with clinical outcome. Netilmicin levels were above the minimal inhibitory concentration of the pathogens in 59 of 64 (92%) drainage fluid specimens in which aerobic bacteria were isolated. Aerobic bacteria were isolated in 91% of drainage fluid specimens if the pH was less than 7.0, compared to 37% if pH was more than 7.0 (p < 0.001). Reduction of pH antagonized aminoglycoside activity in vitro against clinical isolates of Escherichia coli. Surgical reexploration should be considered in cases of deterioration following a laparotomy associated with detection of acidic drainage fluid.