Intra-operative irrigation of the peritoneal cavity with ampicillin in experimental posttraumatic peritonitis

Penetrating abdominal wounds with injury to the intestines were inflicted on 24 anaesthetized pigs. The injured gut was resected. During this operation the peritoneal cavity in 9 pigs was irrigated with 3 litres of antibiotic solution (ampicillin 2 g/l). In 15 pigs the irrigation was done with 3 litres of saline solution only. During the postoperative observation period the animals were in continuous anaesthesia. Absorption of ampicillin, reduction of the peritoneal bacterial flora and emergence of resistant strains were evaluated. Ampicillin was rapidly absorbed to the systemic circulation, with an average peak concentration of 42.4 +/- 1.7 mg/l. The average half-life of the drug in serum was 54 +/- 4 min. The average density of the total aerobic flora decreased during the operation from 10(4.74) CFU/ml peritoneal exudate fo 10(1.20) CFU/ml, but increased to 10(5.16) CFU/ml during the posttraumatic observation period. Total anaerobic counts changed to similar extent. The results were not significantly different from the values in the saline-irrigation group. Ampicillin irrigation led to a significant increase of resistant strains, from 25% before irrigation to 97% at the end of the observation period.