A New Dosing Frontier: Retrospective Assessment of Effluent Flow Rates and Residual Renal Function Among Critically Ill Patients Receiving Continuous Renal Replacement Therapy

In 2020, cefiderocol became the first Food and Drug Administration-approved medication with continuous renal replacement therapy (CRRT) dosing recommendations based on effluent flow rates (Q E). We aimed to evaluate the magnitude and frequency of factors that may influence these recommendations, that is, Q E intrapatient variability and residual renal function. Retrospective observational cohort study. ICUs within Hartford Hospital (890-bed, acute-care hospital) in Connecticut from 2017 to 2023. Adult ICU patients receiving CRRT for greater than 72 hours. CRRT settings including Q E and urine output (UOP) were extracted from the time of CRRT initiation (0 hr) and trends were assessed. To assess the impact on antibiotic dosing, cefiderocol doses were assigned to 0 hour, 24 hours, 48 hours, and 72 hours Q E values per product label, and the proportion of antibiotic dose changes required as a result of changes in inpatient’s Q E was evaluated. Among the 380 ICU patients receiving CRRT for greater than 72 hours, the median (interquartile range) 0 hour Q E was 2.96 (2.35–3.29) L/hr. Approximately 9 Q E values were documented per patient per 24-hour window. Q E changes of greater than 0.75 L/hr were observed in 21.6% of patients over the first 24 hours and in 7.9% (24–48 hr) and 5.8% (48–72 hr) of patients. Approximately 40% of patients had UOP greater than 500 mL at 24 hours post-CRRT initiation. Due to Q E changes within 24 hours of CRRT initiation, a potential cefiderocol dose adjustment would have been warranted in 38% of patients (increase of 21.3%; decrease of 16.6%). Q E changes were less common after 24 hours, warranting cefiderocol dose adjustments in less than 15% of patients. Results highlight the temporal and variable dynamics of Q E and prevalence of residual renal function. Data also demonstrate a risk of antibiotic under-dosing in the first 24 hours of CRRT initiation due to increases in Q E. For antibiotics with Q E-based dosing recommendations, empiric dose escalation may be warranted in the first 24 hours of CRRT initiation.