The Time Course of Catecholamine Dose Reduction in Septic Shock as a Predictor of Bacterial Susceptibility to Empiric Antimicrobial Therapy: A Retrospective Observational Study

<b>Background/Objectives</b>: The 28-day mortality rate for septic shock is high, necessitating rapid and effective empiric antimicrobial therapy. In this study, we investigate whether the rate of catecholamine dose reduction in septic shock can indicate bacterial susceptibility to initial antimicrobial therapy or not. <b>Methods:</b> This retrospective observational study involved 108 adult patients with bacteraemia and septic shock admitted to the intensive care unit of Nihon University Itabashi Hospital between January 2017 and December 2023. They were classified into the Susceptible or Resistant groups based on the bacteria's susceptibility to the initial empiric antimicrobial therapy. Catecholamine dosages were converted to norepinephrine equivalent (NEE) scores, with the time course from the peak to the end of administration measured at NEE reductions. <b>Results:</b> Of the 108 patients, 94 were in the Susceptible group and 14 in the Resistant group. The Susceptible group showed faster reductions in catecholamine doses: the time to reduce the dose from the maximum NEE to 25% was 19 vs. 49.5 h (<i>p</i> = 0.0057), and to 0%, it was 29 vs. 54 h (<i>p</i> = 0.0475). The time to reduce the dose from the maximum NEE to 75% was 8 vs. 12.5 h (<i>p</i> = 0.0733), and to 50% it was 13 vs. 21.5 h (<i>p</i> = 0.1081). <b>Conclusions:</b> In septic shock with bacteraemia, a faster catecholamine dose reduction indicates bacterial susceptibility to the initial empiric antibiotics. This reduction rate can serve as an early clinical indicator of the appropriate initial empiric therapy.