Adjunctive therapy of intravenous colistin to intravenous tigecycline for adult patients with non-bacteremic post-surgical intra-abdominal infection due to carbapenem-resistant Acinetobacter baumannii.

Post-surgical intra-abdominal infections (IAIs) due to carbapenem-resistant Acinetobacter baumannii (CRAB) are difficult to treat due to suboptimal peritoneal penetrations of several antimicrobial agents. Tigecycline has favorable outcomes of treating IAIs due to multidrug-resistant organisms but occurrence of breakthrough bacteremia has been observed because this agent has low serum level. Colistin has in vitro activity against CRAB but data on treatment of IAIs is limited due to poor peritoneal penetration. The purpose of this retrospective study is to explore the outcomes of adjunctive intravenous (IV) colistin to IV tigecycline in the treatment of IAIs caused by CRAB. Of 28 patients with non-bacteremic post-surgical IAIs due to CRAB, 14 patients received IV tigecycline alone and 14 patients received IV tigecycline with IV colistin. The 14-day, 30-day, in-hospital mortality rates, the rate of breakthrough bacteremia and the rate of bacterial eradication were not significantly different. The adjunctive therapy of IV colistin was associated with significantly higher rates of renal complications (10/14) than those receiving IV tigecycline alone (3/14) (P value = 0.023). In addition, the patients receiving adjunctive IV colistin had significantly more unfavorable non-clinical outcomes including longer length of hospital stay (P value = 0.049) and higher antimicrobial cost (P value = 0.008) and non-antimicrobial costs (P value = 0.037). In this study, adjunctive IV colistin to conventional IV tigecycline in the treatment of non-bacteremic post-surgical IAIs caused by CRAB did not yield clinical benefit but caused higher renal complication and unfavorable non-clinical outcomes.