Impact of antibiotic susceptibility reporting on broad spectrum antibiotic use in serratia and morganella bacteremia.

To minimize broad-spectrum antibiotic use, our microbiology laboratory changed antibiotic susceptibility reporting for AmpC-beta-lactamase producing Serratia marcescens and Morganella morganii in blood cultures to include results of narrow spectrum 3rd generation cephalosporins. We assessed the impact of this change on broad-spectrum antibiotic use and clinical outcomes. All adult patients with Serratia marcescens or Morganella morganii in blood culture 2 years pre- and post-change of susceptibility reporting were retrospectively reviewed. Exclusion: more than one pathogen isolated in their blood culture, did not receive antibiotics or died within 48 hours of positive blood culture. Outcomes: Rates of broad-spectrum antibiotic use, in-hospital mortality, clinical response and microbiologic success. There were 30 patients pre-change and 46 patients post-change of reporting. Cefepime use (broad-spectrum) decreased from 46.7% to 6.5% (p < 0.001) and 3rd generation cephalosporin (narrow-spectrum) use increased (3.3% vs 34.8%, p = 0.0013) in the post-change cohort. This demonstrates the potential role of selective susceptibility reporting in antimicrobial stewardship.

Pharmacokinetics of meropenem and piperacillin in critically ill patients with indwelling surgical drains.

Meropenem and piperacillin are two commonly prescribed antibiotics in critically ill surgical patients. To date, the pharmacokinetics of these antibiotics in the presence of indwelling abdominal surgical drains is poorly defined. This was a prospective pharmacokinetic study of meropenem and piperacillin. Serial plasma, urine and surgical drain fluid samples were collected over one dosing interval of antibiotic treatment in ten patients (meropenem, n = 5; piperacillin n = 5). Drug concentrations were measured using a validated high-performance liquid chromatography assay. Median (interquartile range) pharmacokinetic parameter estimates for meropenem were as follows: area under concentration-time curve (AUC), 128.7 mgh/L (95.3-176.7 mgh/L); clearance (CL), 5.7 L/h (5.1-10.5 L/h); volume of distribution (Vd), 0.41 L/kg (0.35-0.56 L/kg); AUC ratio (drain:plasma), 0.2 (0.1-0.2); and calculated antibiotic clearance via surgical drain, 3.8% (2.8-5.4%). For piperacillin, unbound pharmacokinetic results were as follows; AUC, 344.3 mgh/L (341.1-348.4 mgh/L); CL, 13.1 L/h (12.9-13.2 L/h); Vd, 0.63 L/kg (0.38-1.28 L/kg); AUC ratio (drain:plasma), 0.2 (0.2-0.3); and calculated antibiotic clearance via surgical drain 8.2% (3.3-14.0%). A linear correlation was present between the percentage of antibiotic cleared through the drain and the volume of surgical drain fluid output for meropenem (r(2) = 0.89; P = 0.05) and piperacillin (r(2) = 0.63; P = 0.20). Meropenem and piperacillin have altered pharmacokinetics in critically ill patients with indwelling surgical drains. We propose that only when very high drain fluid output is present (>1000 mL/day) would an additional dose of antibiotic be necessary.