Study subjects and measurements

We retrospectively reviewed elderly patients (≥65 years old) treated with CTRX at Higashisumiyoshi Morimoto Hospital between April 2019 and March 2020. First, patients without CT scans before CTRX administration and within nine weeks after CTRX administration were excluded in order to ensure the same background characteristics for comparative cases. Second, patients with a history of cholelithiasis or who had undergone cholecystectomy before CTRX treatment were also excluded. Fig. 1 shows a flowchart of the selection of participants.

Flowchart of participant selection. CT: computed tomography, CTRX: ceftriaxone

We examined the age, sex, body mass index (BMI), CTRX dose, CTRX treatment duration, fasting status, bedridden status, blood test results [creatinine (Cr), estimated glomerular filtration rate (eGFR)], and the day of the CT examination after CTRX administration (CT day) to identify the risk factors for pseudolithiasis. Blood samples were collected before CTRX therapy.