1. Anand Kumar, Cameron Haery, Bhanu Paladugu, Aseem Kumar, Simon Symeoneides, Leo Taiberg, Jailan Osman, Gordon Trenholme, Steven M. Opal, Roy Goldfarb, and Joseph E. Parrillo ABSTRACT Background. This study was designed to examine the relationship between the timing of antibiotic treatment and both survival rates and hemodynamic/inflammatory correlates of survival in a murine model of Escherichia coli septic shock. Methods. Surgical implantation of an E. coli (O18:K1:H7)laced, gelatin capsuleencased fibrinogen clot was used to generate a bacteremic model of murine septic shock. Survival duration, hemodynamic responses, and circulating serum tumor necrosis factor (TNF), interleukin (IL)6, and lactate levels were assessed in relation to increasing delays in or absence of antibiotic treatment. Results. A critical inflection point with respect to survival occurred between 12 and 15 h after implantation. When initiated at or before 12 h, antibiotic treatment resulted in 20% mortality, but, when initiated at or after 15 h, it resulted in >85% mortality. Physiologically relevant hypotension developed in untreated The Duration of Hypotension before the Initiation of Antibiotic Treatment Is a Critical Determinant of Survival in a Murine Model of Escherichia coli Septic Shock: Association with Serum Lactate and Inflammatory Cytokine Levels septic mice by 12 h after implantation. Values for heart rate differed between untreated septic mice and sham-infected control mice by 6 h after implantation, whereas values for cardiac output and stroke volume did not differ until at least 1824 h after implantation. Antibiotic treatment initiated 12 h after implantation was associated with persistence of increased circulating serum lactate, TNF-, and IL-6 levels. Conclusions. The timing of antibiotic treatment relative to hypotension is closely associated with survival in this murine model of septic shock. Delay in antibiotic treatment results in the persistence of inflammatory/stress markers even after antibiotic treatment is initiated. (J Infect Dis 2006; 193: 251-258)

2. The Duration of Hypotension before the Initiation of Antibiotic Treatment Is a Critical Determinant of Survival in a Murine Model of Escherichia coli Septic Shock: Association with Serum Lactate and Inflammatory Cytokine Levels Kumar et al. J Infect Dis 2006; 193: 251-258 Sham infected 0 hr 12 hr 15 hr 18 hr No RX 6 hr Hours after implantation Cumulative survival rate (%)

3. Duration of Hypotension before Initiation of Antibiotic Treatment Is a Critical Determinant of Survival in a Murine Model of Escherichia coli Septic Shock: Association with Serum Lactate and Inflammatory Cytokine Levels Mean cardiovascular responses in untreated septic mice (white circles; n = 10) and sham-infected control mice (black circles; n = 8). Measurements taken of heart rate (HR; A), stroke volume (SV; B), cardiac output (CO; C), and mean arterial pressure (MAP; D). Group comparisons made using repeated-measures analysis of variance; point comparisons made using least-squares method. *P <.05, vs. sham-infected control mice at equivalent time point; P <.0001, vs. sham-infected control mice at equivalent time point. Error bars indicate SEs. Kumar et al. J Infect Dis 2006; 193: 251-258

4. Duration of Hypotension before Initiation of Antibiotic Treatment Is a Critical Determinant of Survival in a Murine Model of Escherichia coli Septic Shock: Association with Serum Lactate and Inflammatory Cytokine Levels Kumar et al. J Infect Dis 2006; 193: 251-258

5. Duration of Hypotension before Initiation of Antibiotic Treatment Is a Critical Determinant of Survival in a Murine Model of Escherichia coli Septic Shock: Association with Serum Lactate and Inflammatory Cytokine Levels Kumar et al. J Infect Dis 2006; 193: 251-258

6. Duration of Hypotension before Initiation of Antibiotic Treatment Is a Critical Determinant of Survival in a Murine Model of Escherichia coli Septic Shock: Association with Serum Lactate and Inflammatory Cytokine Levels Kumar et al. J Infect Dis 2006; 193: 251-258

7. Duration of Hypotension before Initiation of Antibiotic Treatment Is a Critical Determinant of Survival in a Murine Model of Escherichia coli Septic Shock: Association with Serum Lactate and Inflammatory Cytokine Levels Kumar et al. J Infect Dis 2006; 193: 251-258

8. The Duration of Hypotension before the Initiation of Antibiotic Treatment Is a Critical Determinant of Survival in a Murine Model of Escherichia coli Septic Shock: Association with Serum Lactate and Inflammatory Cytokine Levels Mean serum lactate (A), tumor necrosis factor (TNF) (B), and interleukin (IL)6 (C) levels in untreated septic mice (white inverted triangles) and sham-infected control mice (black circles; n = 8 mice/group). Group comparisons were made using repeated-measures analysis of variance; point comparisons were made using the least-squares method. Septic mice vs. sham-infected control mice, P <.0001 in all cases. P <.0001, vs. sham-infected control mice at the equivalent time point. Error bars indicate SEs. Kumar et al. J Infect Dis 2006; 193: 251-258 Sham-infected mice Septic mice 500 400 300 200 100 0 800 0 600 0 400 0 200 0 0 0 2 4 6 8 10 12 14 Hours after implantation 0 h6 h 12 h 18 h 24 h 18 h 12 h 6 h 24 h 0 h Serum lactate (mmol/L) Serum TNF-α (pg/mL) Serum IL-6 (pg/mL) Sham-infected mice Septic mice Sham-infected mice Septic mice

9. The Duration of Hypotension before the Initiation of Antibiotic Treatment Is a Critical Determinant of Survival in a Murine Model of Escherichia coli Septic Shock: Association with Serum Lactate and Inflammatory Cytokine Levels Kumar et al. J Infect Dis 2006; 193: 251-258

10. The Duration of Hypotension before the Initiation of Antibiotic Treatment Is a Critical Determinant of Survival in a Murine Model of Escherichia coli Septic Shock: Association with Serum Lactate and Inflammatory Cytokine Levels Kumar et al. J Infect Dis 2006; 193: 251-258

11. The Duration of Hypotension before the Initiation of Antibiotic Treatment Is a Critical Determinant of Survival in a Murine Model of Escherichia coli Septic Shock: Association with Serum Lactate and Inflammatory Cytokine Levels Kumar et al. J Infect Dis 2006; 193: 251-258

12. Treatment 6 h after implantation Treatment 12 h after implantation Treatment 18 h after implantation Before treatment 3 h after treatment 6 h after treatment Before treatment 3 h after treatment 6 h after treatment Before treatment 3 h after treatment 6 h after treatment 12 10 8 6 4 2 0 700 600 500 400 300 200 100 0 8000 6000 4000 2000 0 Serum IL-6 (pg/mL) Serum TNF-  (pg/mL) Serum lactate (mmol/L) The Duration of Hypotension before the Initiation of Antibiotic Treatment Is a Critical Determinant of Survival in a Murine Model of Escherichia coli Septic Shock: Association with Serum Lactate and Inflammatory Cytokine Levels Mean serum lactate (A), tumor necrosis factor (TNF) (B), and interleukin (IL)6 (C) levels in mice given antibiotic treatment 6 (black bars), 12 (light gray bars), or 18 (dark gray bars) h after implantation (n = 6 mice/group). Highly significant differences in responses between groups existed (P <.0001). Group comparisons were made using repeated-measures analysis of variance; point comparisons were made using the least-squares method. *P <.05, vs. septic mice before antibiotic treatment at the same treatment initiation time point; P <.0001, vs. septic mice before antibiotic treatment at the same treatment initiation time point. Error bars indicate SEs. Kumar et al. J Infect Dis 2006; 193: 251-258

13. The Duration of Hypotension before the Initiation of Antibiotic Treatment Is a Critical Determinant of Survival in a Murine Model of Escherichia coli Septic Shock: Association with Serum Lactate and Inflammatory Cytokine Levels Kumar et al. J Infect Dis 2006; 193: 251-258

14. The Duration of Hypotension before the Initiation of Antibiotic Treatment Is a Critical Determinant of Survival in a Murine Model of Escherichia coli Septic Shock: Association with Serum Lactate and Inflammatory Cytokine Levels Kumar et al. J Infect Dis 2006; 193: 251-258

15. The Duration of Hypotension before the Initiation of Antibiotic Treatment Is a Critical Determinant of Survival in a Murine Model of Escherichia coli Septic Shock: Association with Serum Lactate and Inflammatory Cytokine Levels Kumar et al. J Infect Dis 2006; 193: 251-258

16. Treatment 0 h after implantation Treatment 6 h after implantation Treatment 12 h after implantation Treatment 18 h after implantation 6 h after treatment 6 h after treatment Before treatment Before implantation 0.01 0.1 1 10 100 1000 Serum LPS (pg/mL) The Duration of Hypotension before the Initiation of Antibiotic Treatment Is a Critical Determinant of Survival in a Murine Model of Escherichia coli Septic Shock: Association with Serum Lactate and Inflammatory Cytokine Levels Kumar et al. J Infect Dis 2006; 193: 251-258

17. The Duration of Hypotension before the Initiation of Antibiotic Treatment Is a Critical Determinant of Survival in a Murine Model of Escherichia coli Septic Shock: Association with Serum Lactate and Inflammatory Cytokine Levels Kumar et al. J Infect Dis 2006; 193: 251-258 0h6h12h18h24h CO  SV↓ Lactate↑↑ Early septic shock MAP↓ Lactate↑ HR↑ TNF-  ↑ IL-6↑ Implantation