Early Oral Step-Down Versus Continued Intravenous Antibiotic Treatment of Complicated Intra-Abdominal Infection

<b><i>Background:</i></b> Complicated intra-abdominal infections (cIAIs) require a combined tactic, of source control and antimicrobial therapy. This study aimed to evaluate the safety and efficacy of oral step-down antimicrobial therapy in cIAIs after initial intravenous (IV) antimicrobial therapy. <b><i>Methods:</i></b> This retrospective cohort study included hospitalized adult patients diagnosed with a cIAI who received more than seven days of IV therapy from March 2017 to October 2021. Exclusion criteria included primary/peritoneal dialysis-related peritonitis, necrotizing pancreatitis, fistulizing inflammatory bowel disease, or upper gastrointestinal tract infection. Patients were assigned into two groups: IV-only or oral step-down therapy. The primary outcome was infection recurrence, defined as re-initiation of antimicrobial agents after a treatment-free period of more than or equal to three days. Secondary outcomes included treatment escalation, repeat source control procedure, treatment-related complications, and all-cause mortality. <b><i>Results:</i></b> The cohort consisted of 248 patients (199 IV-only and 49 oral step-down). Patients receiving IV-only therapy had a shorter median antimicrobial duration than the oral step-down group (13 vs. 23 d; p <0.0001). Infection recurrence occurred in 26 (13.1%) and 6 (12.2%) patients in the IV-only and oral step-down groups, respectively (p = 0.88). Treatment escalation, repeat source control, and 28-day mortality were similar between groups. Oral step-down therapy resulted in more adverse drug events (10.2% vs. 3.0%; p = 0.04). <b><i>Discussion:</i></b> Transition to oral step-down after initial IV therapy had a similar rate of infection recurrence as IV-only therapy but was associated with a longer duration of antimicrobial therapy and an increased rate of adverse drug reactions. Larger randomized non-inferiority studies are needed to confirm this approach.