Acute cholangitis (AC) is a potentially life-threatening bacterial infection commonly encountered in clinical practice. Mortality in severe AC can be as high as 20 %; however, this can be reduced with timely and appropriate interventions [1,2]. Therefore, the appropriate assessment of disease severity, interventions, and antimicrobial therapy is critical.

AC often leads to the development of bacteremia, which is attributed to a combination of bile colonization and increased bile duct pressure [3]. The incidence of bacteremia in AC has been reported to range from 21 to 71 % worldwide [4]. The mortality rate of bacteremia in AC reaches 8 % with adequate empiric therapy and 27 % with inadequate therapy; i.e., antibiotics to which the causative pathogens are not susceptible [5]. Thus, it is important to select appropriate empiric therapy based on the pathogens detected in the blood cultures of patients with AC.

The Tokyo Guidelines for the Management of AC and cholecystitis were established in 2007 and subsequently revised twice [6]. The Tokyo Guidelines 2018 (TG18) recommend the use of antibiotics for community-acquired infections, classified by severity, and healthcare-associated infections. However, no indications regarding the priority of antibiotic use are provided [7].

Cefmetazole (CMZ), an antibiotic with limited international distribution, is recommended for the treatment of non-severe AC by the TG18. CMZ belongs to the cephamycin class and has a relatively narrow spectrum of activity against Enterobacterales compared to that of ceftriaxone. However, these compounds are also active against anaerobes. CMZ is stable against hydrolysis by extended-spectrum β-lactamases (ESBL) and has shown clinical benefits in observational studies of infections caused by ESBL-producing bacteria [8]. In AC, the isolation of ESBL-producing bacteria has been reported to be a risk factor for organ dysfunction and it increases 30-day mortality [9,10]. Therefore, the use of CMZ as an empirical AC treatment might be beneficial. Nevertheless, CMZ-non-susceptible (CMZ-NS) bacteria are sometimes isolated from blood cultures of patients with AC, and it remains unclear which patients are inappropriate for empiric CMZ treatment. Therefore, we aimed to investigate the risk factors for CMZ-NS bacteremia and evaluate mortality in patients with AC.